I am terrified about the recent talk about poles reversing and 2012. Do I need to prepare myself and accept this?

In late December 2012, three planets will line up correct? And the earth will pass next to the black hole in orion’s belt, and turn our planet upside down. My question is, will the earth’s gravity withstand it and hold us up and the oceans from going wild?

According to NASA scientists, the earth will stand still for about three days and then, in one hour, rotate a full 90 degrees (the geographical pole shift) during which time winds will be an average of 200 miles per hour. Every volcano on earth will erupt and of course there will be many earthquakes, so two thirds of earth’s population will die in that one hour. Is this true??

How can an astrobiologist have anything to say scientifically about nibiru, the Shumerian planet? With scientists around the world finding facts in the existing scriptures on everything else, including Pluto, then why would we not believe them about nibiru? How can we say nibiru doesn’t exist if science is only in the past few decades catching up with a science that has existed before civilized man?

There are various recent pictures and videos of an unidentified object that is beside the sun. If it is not Planet X what is it? I myself took a picture of the sun and have also captured the same object.

I am a legal administrative assistant and, having done my share of investigation, I find that the fact that the sun will pass in front of the earth and roughly eclipse the black hole at the centre of the Milky Way on Dec 21, 2012 decidedly compelling. There seems to be so much real evidence supporting the fact that something extraordinary is happening or going to happen, that I cannot simply dismiss it.

If Nibiru is a hoax, please explain to me why have you not tried to confirm this with the media to at least drain some fear out of the many people who are falling for this hoax.

Someone has said that the Nibiru can be visible by our eyes since 15th May 2009 in south hemisphere. Someone also said that you, NASA have known this planet X, Nibiru since 1983. I really feel afraid of the end of world. Please tell me the truth!!

Why NASA is hiding facts about nibiru? It really exists beyond pluto. There is photo proof for that. It seems to me that you and NASA hide something big.

I am from Pakistan, and here the propaganda of 2012 is rising day by day. A lot of people is doing business from 2012. My question is why is NASA not condemning these hoax?

Why doesn’t you and your government put a ban on the TV shows and report telecasting about Nibiru? If US can step to protect the world physically from terrorism, why can’t it protect us mentally from these news, if they are hoax?

If you claim that the nibiru planet is a hoax why is there actual footage from the nasa stating that the planet exists?

I am a Russian journalist. We in this country have many people who are anxious about problem Nibiru. I know that serious scientists including in the USA do not accept Nibiru theory of Zecharia Sitchin. But tell, please, who from the scientific USA does not support even the existence of Nibiru?

I don’t believe NASA. Nibiru will throw modern-day science as we know it for a loop. NASA knows it’s there, but all will be revealed soon. . . . So why are you not telling the truth? Please answer me, I’m a boy, and I’m 16 years old.

If Nibiru is such a hoax then why was it on the History Channel and why don’t you guys have censors for such “hoaxes” then? I have four little babies and I think all of the human race deserves to know the truth from you “experts”. If it’s real then do the right thing; if not quit letting these hoaxes confuse true issues please.

This story began with predictions that Nibiru, supposedly a planet discovered by the Sumerians, is headed toward Earth. Zecharia Sitchin, who writes fiction about the ancient Mesopotamian civilization of Sumer, claimed in several books (e.g., The Twelfth Planet, published in 1976) that he has found and translated Sumerian documents that identify the planet Nibiru, orbiting the Sun every 3,600 years. Sitchin has sold many books about these Sumerian fables, which include stories of “ancient astronauts” called the Anunnaki who aided the Sumerians. Then Nancy Lieder, a self-declared psychic who claims she communicates with aliens, wrote on her Web site ZetaTalk that inhabitants of a fictional planet around the star Zeta Reticuli warned her that the Earth was in danger from Planet X, or Nibiru. This catastrophe was initially predicted for May 2003, but when nothing happened, the doomsday date was moved to December 2012.

These two Nibiru fables were greatly amplified when linked with the turn-over of the Mayan long-count calendar at or near the winter solstice of 2012. Many Web sites sprang up declaring that December 21, 2012, would be the end of the world, a time of violent physical and spiritual transformation—never mind that the real end for Mayan civilization came several hundred years earlier with the European invasion of the Americas. This spring I counted more than 175 books on the 2012 doomsday listed on Amazon.com, where the most popular themes are the Mayan calendar and ways to survive the coming apocalypse.

Of course, Nibiru does not exist. A large planet (or a brown dwarf) in our solar system would have been known to astronomers for decades, both indirectly from its gravitational perturbations on other objects and by direct detection in the infrared. The NASA Infrared Astronomy Satellite (IRAS) carried out the first all-sky survey in 1983, which, along with several subsequent surveys, would have seen Nibiru if it was there. However, the Nibiru proponents have asserted that Nibiru was hiding—that it remained behind the Sun for several years or that it could be seen only from the South Pole. Both of these are geometrically absurd statements. Most of the so-called Nibiru photos on the Web are lens flare produced when a camera points at a bright source, an artifact also responsible for many UFO photos. As it approaches Earth, of course, Nibiru should be increasing in brightness. In fact, if it were going to be inside Earth’s orbit in three years, it should have already reached naked-eye visibility, and tens of thousands of astronomers, both amateur and professional, would be tracking it.

As the story grows in complexity, many more doomsday scenarios are being suggested, often unrelated to Nibiru. These include a reversal of the Earth’s magnetic field, severe solar storms associated with the eleven-year solar cycle (which may peak in 2012), a reversal of Earth’s rotation axis, a 90 degree flip of the rotation axis, bombardment by large comets or asteroids, and bombardment by gamma rays or various unspecified lethal rays coming from the center of the Milky Way Galaxy or the “dark rift” seen in a nearby galactic spiral arm. A major theme has become celestial alignments, which fascinate laypersons. Supposedly, the Sun will align with the galactic center (or maybe with the Milky Way Dark Rift) on December 21, 2012, subjecting us to potentially deadly forces.

All of these pseudoscientific claims, together with distrust of the government, are being amplified by publicity for the new film from Columbia Pictures, titled simply “2012,” to be released in November 2009. The film’s trailer, appearing in theaters and on its Web site www.whowillsurvive2012.com, shows a tidal wave breaking over the Himalayas with only the following words: “How would the governments of our planet prepare 6 billion people for the end of the world? [long pause] They wouldn’t. [long pause] Find out the Truth. Google search 2012.”

The film publicity includes creation of a faux scientific Web site for “The Institute for Human Continuity,” which is entirely fictitious. According to this Web site, the IHC is dedicated to scientific research and public preparedness. Its mission is the survival of mankind, and the Institute was supposedly founded in 1978 by international leaders of government, business, and science. In 2004, it claims, IHC scientists confirmed with 94 percent certainty that the world would be destroyed in 2012. This Web site encourages people to register for a lottery to select those who will be saved; a colleague of mine submitted the name of her cat, which was accepted. I learned from Wikipedia that creating fake Web sites is a recent advertising technique called viral marketing, analogous to computer viruses.

The Nibiru 2012 hoax was initially spread by the Internet. Now at least one TV cable show per week deals with this coming apocalypse. Most of these seem to be on the History Channel and the Discovery Channel. Much of the recent coverage focuses on Nostradamus (who else?), who is now credited with predicting doomsday in 2012. The story has also been reported on Fox News, and I anticipate intensified media coverage over the next three years.

The doomsday scenario is spreading internationally; about half the questions I receive about Nibiru/2012 on my Web site now come from outside the U.S. Many write from India, saying they read about Nibiru in the newspapers. A journalist said that many people in Russia “are anxious by problem Nibiru.” A correspondent from Pakistan wrote, “The propaganda of 2012 is rising day by day. Why is NASA is not condemning these hoax?” The theme of censorship is often raised. One woman asked “why you and your government dont put a ban on the TV shows and report telecasting about Nibiru and 2012. If US can step to protect the world physically from terrorism, why can’t it protect us mentally from these news, if they are hoax?” Another woman pleaded, “I have four little babies and I think all of the human race deserves to know the truth from you ‘experts’. If it’s real then do the right thing; if not quit letting these hoaxes confuse true issues please.”

I continue to receive several email questions every day about Nibiru and 2012, sent to the NASA Web site “Ask an Astrobiologist”. See the sidebar for some examples received during just two weeks in May 2009. Many questioners are frightened, angry, or both. To my surprise, I have not seen much evidence that other scientists or skeptics are concerned about this growing outbreak of pseudoscience. More than a hundred past replies of mine are posted on the astrobiology Web site and also referenced on the NASA home page. A few news blogs such as Yahoo also provide truthful answers, but these are drowned out by the 2012 hysteria. I give credit to Wikipedia, which has several entries on Nibiru, including a very good overview of the pseudoscience under “Nibiru collision.” But questions keep streaming in, and I fear this will not be my last update on this subject.

Popular UFO claims include alien bases on the Moon and Mars. It is widely (but falsely) reported that Buzz Aldrin saw a UFO on the Apollo 11 flight and that NASA spacecraft discovered a humanoid face and other artifacts on Mars.

Much of the public believes that UFOs are alien spacecraft. This represents a conceptual leap from unidentified lights in the sky or radar bogies that were the UFO stories when I was growing up. Today, “believers” are talking about actual alien contact, with alien bases on the Moon and Mars, and their concerns receive reinforcement from radio, TV, and Internet blogs.

On one level UFOs are real, of course; many people occasionally see objects in the sky that are not immediately identifiable as planes, balloons, planets, stars, or unusual atmospheric phenomena. But the questions I receive from the public (submitted to a NASA Web site) suggest a belief system linking UFOs with alien visitations and abductions spiced up by “conspiracy theories” to hide this information from the public.

If UFOs are alien spacecraft visiting Earth, then it seems reasonable that evidence of alien civilizations might be seen by astronomers or the radio signals from alien spacecraft might be picked up by the sensitive receivers we use to communicate with our own spacecraft. Perhaps astronauts who venture into space would be among the first to make reliable observations of alien spacecraft or artifacts. Perhaps we should look for alien bases on other worlds. Indeed, the Internet carries many stories of such encounters. I will examine some of the evidence cited for alien presence in the solar system.

Astronaut Encounters with Aliens

One allegedly well-documented report stems from an interview in which astronaut Buzz Aldrin describes seeing a UFO during the Apollo 11 mission. In an interview on the Science Channel (left, top), Aldrin stated that he, Neil Armstrong, and Mike Collins saw unidentified objects that appeared to follow their Apollo spacecraft.

To get the story straight, I called Buzz Aldrin, who was happy to explain what happened. He said that his remarks were taken out of context to reverse his meaning. It is true that the Apollo 11 crew spotted an unidentified object moving with the spacecraft as they approached the Moon. After they verified that this mystery object was not Apollo 11’s large rocket upper stage, which was about 6,000 miles away by then, they concluded that they were seeing one of the small panels that had linked the spacecraft to the upper stage (any part of the spacecraft’s rocket upper stage will continue to move alongside the spacecraft, as both are floating in free-fall). These panels were too small to track from Earth and were relatively close to the Apollo spacecraft. Aldrin told me that they chose not to discuss this on the open communications channel since they were concerned that their comments might be misinterpreted. His entire explanation about identifying the panels was cut from the broadcast interview, giving the impression that the Apollo 11 crew had seen a UFO. Aldrin told me that he was angry about the deceptive editing and asked the Science Channel to correct the intentional twisting of his remarks, but they refused. Later, Aldrin explained what happened on CNN’s Larry King Live (left, bottom) but was nearly cut off by the host before he could finish.

With the popularity of YouTube, this same question is addressed to me repeatedly, as in: “Check out this video on YouTube with Buzz Aldrin saying he saw a UFO on Apollo 11. Who is fibbing? NASA or the great American hero, Buzz Aldrin?” My answer was that the fibbing was being done by the producers of the video, who omitted the second half of the interview.

It is instructive to watch this interview to see the ways the story is embellished and ultimately manipulated. Most of the talking is done by the interviewer and not Aldrin, but their comments have been edited to create the illusion of a seamless narrative. Throughout the interview we see a montage of short scenes from Apollo and other missions, including a blurry image through the window taken during a later flight. Only a critical viewer will distinguish what Aldrin said from the narrative by the interviewer or realize that the video clips are unrelated. The end product is clever disinformation, strongly suggesting—without explicitly lying—that Aldrin and his crewmates saw an alien spacecraft.

Many Internet claims of encounters between NASA astronauts and alien spacecraft are based on quotes from “secret communications” between flight crews and Houston. It is true that there are such private conversations, concerning crew health for example. But the Internet stories of overheard conversations are never documented and often attributed to leaks from unnamed NASA workers whose jobs (or even lives) would allegedly be at risk if they were identified. Many of these stories involve the Apollo 11 flight, and they include claims that alien spaceships accompanied the NASA craft during its Moon landing and that a row of alien spacecraft along a crater rim monitored the astronauts’ spacewalk on the lunar surface. (Incidentally, Apollo 11 landed on a flat plain where there were no hills or crater rims to provide such a viewpoint.)

To my knowledge, no NASA astronaut has ever reported seeing a UFO in space, let alone having a confrontation with aliens. However, this is not to say that no astronaut believes that alien visitations to Earth might be happening. Recently there were news reports that Apollo 14 astronaut Edgar Mitchell believes in the reality of some reports of UFOs. He has attended a number of meetings of UFO believers, and he asserts that some of these reports are true, and that the U.S. government and military are aware of these alien visits. However, Mitchell does not claim to have seen aliens himself. His astronaut colleagues tell me that he has always had an interest in the occult, and he even tried to conduct a parapsychology experiment on the way to and from the Moon. It is easy for a journalist to ignore Mitchell’s caveats about most UFO reports being untrue, or about not encountering an alien himself, to give the impression that he and other astronauts have had frequent encounters with beings from other worlds.

One argument presented to me by several correspondents is that aliens must have warned humans to stay away from their bases on the Moon. Otherwise, why was the Apollo program suddenly terminated with three more missions scheduled and almost ready for launch? (The huge Apollo/Saturn-5 rockets that enthrall visitors to the NASA space parks at Canaveral, Houston, and Huntsville are not mock-ups; they are real hardware built for Apollo 18, 19, and 20.) The conspiracy story attributes our failure to follow up on the Apollo flights to this same interplanetary quarantine and suggests that NASA’s current program to return astronauts to the Moon will be cancelled for the same reason. I admit being baffled by the sudden termination of the Apollo program at the peak of its success, but I accept the official explanation that it was due to the changing political priorities of the Nixon administration, where many looked upon Apollo as a Kennedy-Johnson program.

Mars: The Viking Era

Mars plays a unique role in public consciousness. Just a century ago, this planet was widely thought to be inhabited by intelligent creatures, largely due to astronomical studies and the popular writing of Percival Lowell. The classic science-fiction novel War of the Worlds by H.G. Wells reinforced public curiosity about the possibility of aliens on Mars. But early space missions that showed decisively that Mars was not really very Earth-like—with no canals and an atmosphere only 1 percent the size of ours—damped much of the public’s fascination. Scientific interest has steadily increased, however, and Mars is the planet most visited by spacecraft. The first stage of scientific exploration climaxed in 1976 with two identical Mars landers and orbiters as part of the Viking program. All four Viking spacecraft were fabulously successful, providing a comprehensive survey of the planet together with detailed analysis at two landing sites, including clever experiments to search for evidence of microbial life.

After two decades of post-Viking neglect, NASA initiated a new series of Mars missions with the 1996 Mars Pathfinder, which included a rover about the size of a microwave oven. After two mission failures in 1998, several remarkably successful orbiters and the two famous Mars Exploration Rovers, Spirit and Opportunity, followed. In addition to high-resolution orbiting cameras, there is also a digital, global topographic map based on laser ranging between the orbiter and the surface. As a result, we have more detailed and quantitative data on martian topography than we do for much of the Earth’s surface.

Naturally, the tens of thousands of high-resolution photos from orbit and on the ground (all publicly available) have been studied for evidence of life and any potential artifacts of a possible ancient civilization. In this respect, the most famous discovery was made by Viking Orbiter 1 in 1977, in a low-resolution (about 40 meters) photo of the ancient Cydonia region of Mars. In the midst of a heavily eroded plain with irregular low mountains or mesas is the Face on Mars, one of the iconic images of the space program.

The Face on Mars, seen under oblique lighting, seems to be an oval humanoid face with eyes, nose, and a mouth. It is about one kilometer across and surrounded by a sort of halo that reminds some of the cloth headpiece worn by Egyptian pharaohs. It was spotted by Viking scientist Toby Owen and released to the press as a joke to show how even on Mars we (humans) could find features that looked vaguely like ourselves. Unfortunately, Viking project scientist Jerry Soffen made an offhand remark to the press that this “face” showed up only under this particular lighting and not in other photos of the same site. The problem was that Viking had not taken other photos of this spot at equal or higher resolution, and the mission ended before this area could be mapped again. Thus began another conspiracy theory: NASA was suppressing confirming photos of the face. When the next NASA mission to photograph Mars (Mars Observer) failed in 1992 shortly before its arrival at the Red Planet, the story began to circulate that this failure was faked and the spacecraft was really in orbit and sending back secret high-resolution images of the face.

The Face on Mars has been vigorously promoted by one energetic entrepreneur: Richard C. Hoagland. A young freelance journalist and one-time museum guide, Hoagland was a part of the large corps of journalists who encamped at the Jet Propulsion Laboratory (JPL) for the Viking landings. Hoagland not only accepted the artificial origin of the face, he went on to develop a detailed “theory” that linked this feature with a number of others in Cydonia that he also interpreted as artificial. These included a set of intersecting low ridges that he called the “city” and several mountains of roughly pyramid shape. (Pyramid-shaped peaks with three or four sides are a rather common product of both ice and wind erosion on Earth.)

As improving technology allowed for higher photo resolution, the “face on Mars” looked less like a face and more like the natural landform it is.

Hoagland set out to study the geometry of this layout, finding coincidences in the angles between the features that further demonstrated (to him) their artificial origin. He published the results from his “research” in a 350-page book called The Monuments of Mars (now in its fifth edition). He also undertook a lecture circuit that climaxed when a naïve public affairs officer at NASA Glenn (then Lewis) Research Center in Cleveland invited him to present a director’s seminar and then offered to put a videotape of this talk on the NASA TV channel. Hoagland also began making regular appearances on Art Bell’s late-night talk show Coast to Coast AM, where he still happily holds forth on the conspiracies of NASA and the U.S. government to keep the truth from the public.

Hoagland’s elaborate interpretation of the “monuments” on Mars represents an amazing flight of imagination. Since the features are in a state of ruin, he concludes that the aliens who built them are no longer present and dates the construction of these huge projects to about half a million years ago. Since the face is (in his opinion) clearly human and directed upward (best seen from above), he concludes that it was built as a message for Homo sapiens, a species that was just emerging on Earth at the time. The story then bifurcates: either these aliens were also visiting Earth at the time and knew about the future rise of humans (analogous to the opening sequences in the book and film 2001, A Space Odyssey), or the monuments themselves were built by an earlier race of humans that had moved from Earth to Mars and left no traces of their tenure on our planet. Yet another option is that Homo sapiens had a martian origin, migrating to Earth when their own planet became uninhabitable (a conclusion that flies in the face of all modern genetic analysis of humans and their primate cousins).

Hoagland’s analysis of the geometric patterns of the alleged monuments convinced him that the entire layout in Cydonia was a technical message to humans, one that included the key to a limitless source of energy. Apparently he has deciphered the message but is not revealing it just yet, other than to say that this energy could be tapped only at latitude 19.5 degrees (north or south) on the Sun as well as Earth and Mars. More recently, Hoagland linked the monuments on Mars with the crop circles appearing on Earth, which also allegedly held the key to unlimited energy, implying that the creators of the city on Mars were also active today on Earth. The fact that Hoagland was able to peddle this bizarre fairy tale for two decades and make a living selling books and videotapes is a testament to his ability as a salesman, if not to his unscientific acumen.

The two-decade post-Viking hiatus from Mars provided plenty of time for Hoagland to market his fantasy. The 1992 failure of Mars Observer, far from ending this story, was twisted by Hoagland into an additional conspiracy theory. The day the failure was announced, a group of his followers demonstrated outside the JPL gates to protest the blanket of secrecy they claimed had been thrown over this mission whose real purpose was to allegedly study the face. In the late 1990s, one of the two most frequently asked questions in letters and emails received by NASA concerned the Face on Mars (the other topic was asteroid impacts).

New Results from Mars

In 1998, a much-improved camera arrived at Mars on the Mars Global Surveyor orbiter. A vocal segment of the public demanded that NASA give high priority to re-photographing the face. NASA wisely argued that this was not a high-priority target but quietly obtained a high-resolution image of the face as soon as the spacecraft orbit permitted it. On April 5, 1998, when the Mars Global Surveyor flew over Cydonia for the first time, Michael Malin and his Mars Orbiter Camera (MOC) team snapped a picture ten times sharper than the original Viking photos, revealing a natural landform. However, the new lighting was very different from that of the original Viking photo, and some face proponents refused to believe that this was really the same feature. On April 8, 2001, the MOC captured a photo using the camera’s maximum resolution, better than two meters, which was twenty times higher than the Viking original. This spacecraft also carried another instrument, a laser ranging device, which gradually built up an extremely detailed quantitative topographic map of Mars that did not depend on lighting angles. With these data, it was possible to reconstruct exactly how the mesa would look from any direction. Many details of this story are recounted in the article “Unmasking the Face on Mars”.

Additional images with even higher resolution were obtained in 2007 by the University of Arizona HiRISE camera on the NASA Mars Reconnaissance Orbiter. With a resolution of 25 cm, these photos showed features as small as a briefcase. Such data eventually convinced almost everyone that the face was simply a mesa surrounded by an apron of eroded debris. NASA’s chief Mars scientist, Jim Garvin, even jokingly plotted a hiking trail that ascended the rugged hill. However, as the true nature of this eroded mesa became undeniable, the suggestion was made that the face had been intentionally destroyed by NASA: the clandestine mission of Mars Observer had been to first photograph the feature in detail, then deface it with a well-aimed nuclear missile.

Meanwhile, Richard Hoagland was moving on and generating new claims, some even more bizarre than those associated with the face. The Wikipedia article on Hoagland mentions his assertions that “Rocks on Mars containing biological fossils were purposely destroyed by NASA’s rover Opportunity. Numerous objects surrounding the landing sites of the Mars Exploration Rovers are in fact pieces of martian machinery. There are large semitransparent structures constructed of glass on the lunar surface, visible in some Apollo photography. There is a clandestine space program, using antigravity technology reverse-engineered from lunar artifacts and communicated by secret societies. Federal agencies such as FEMA and NASA are linked to Freemasonry.”

Hoagland held a press conference at the National Press Club on October 30, 2007, to “review NASA’s 50 years of cover-ups and hidden solar system data.” His accusations against NASA appeared in more detail in his book with Mike Bara, Dark Mission: The Secret History of NASA. He was also by then in his crop circle phase, promoting new sources of energy revealed to him in the crop circles. And he is still a regular guest on Coast to Coast AM, where he has the title of science advisor.

Humans have a natural tendency to see anthropomorphic features in natural shapes such as clouds and mountains. As thousands of new photos of the martian surface were streaming back from the rovers, some of these tendencies were bound to pop up. One of the funniest is an image of a tiny eroded rock only a few centimeters long that looks rather like the famous “little mermaid” statue in Copenhagen Harbor. This too has been hailed as a real photo of a Martian. The continuing torrent of spacecraft images from current missions to Saturn and Mercury as well as Mars will probably generate new advocates for aliens in space. Fortunately, the vast majority of people are happy to accept these images as wonderful products of our space age exploration of the solar system and not as a new episode in the great alien cover-up.

Skeptical Inquirer readers may not be aware that a rogue planet on a 3,600-year orbit is about to enter the inner solar system and visit a catastrophe upon Earth. This threatening planet was discovered by the ancient Mesopotamians, who named it Nibiru. It was known also to the Mayans, who associated it with the end—December 2012—of their “long count” calendar. Although astronomers and space scientists are tracking Nibiru, this information is being kept from the public as part of a worldwide conspiracy. This official silence cannot be maintained for much longer, however, since by 2009 Nibiru will be visible to the naked eye from the southern hemisphere, and already Earth’s axis is tilting, changing the length of the day under its influence. As one aficionado recently wrote to me: “Why are you lying? It’s coming, and everyone knows it.”

I was introduced to this conspiracy theory in December 2007, when I began to receive questions about Nibiru submitted to NASA’s “Ask an Astrobiologist” Web site. I normally receive about a dozen questions per week from the public dealing mostly with life in the universe, but sometimes they include UFOs and visiting aliens. Nibiru seemed different, since it was claimed to be an actual planet that was being tracked by astronomers but hidden from the public. Knowing that the astronomers of the world, both professional and amateur, are a free-spirited group who couldn’t keep a secret even if ordered to, I assumed that Nibiru was the sort of Internet rumor that would quickly pass.

However, I also remembered that Nibiru had briefly been prominent among conspiracy buffs in 2003, when there was a similar rumor of the coming destruction of our civilization. The source of this information was a specific warning said to have been sent to the people of Earth by an advanced alien civilization on a planet orbiting the star Zeta Reticuli. A woman named Nancy Lieder claimed to be channeling this information from the Zetans, who warned that a worldwide cataclysm would strike the Earth in May 2003. Phil Plait described this situation in detail on his “Badastronomy” Web site. As it turned out, May 2003 passed with no pole shift or other cataclysms, so I figured that would end the Nibiru interest. Yet here it was again, the same story recycled with an end-of-the-world date reset to December 2012.

In the six months since I first mentioned Nibiru on my Web site, this topic has threatened to take over “Ask an Astrobiologist.” I now receive at least one question per day ranging from anguished (“I can’t sleep; I am really scared; I don’t want to die”) to the abusive (“Why are you lying; you are putting my family at risk; if NASA denies it then it must be true”).

This article is based on more than one hundred questions submitted in the first four months of 2008, only a few of which were actually answered online. Except for some condensing, I’ve left the questioners’ text as it was originally submitted.

Initial Questions: The Distinction between Nibiru, Planet X, and Eris

Although the name of the Sumerian god Nibiru is most often given to this object, I quickly learned that some Web sites were also calling it Planet X or Eris. Planet X is a generic term used by astronomers over the past century for any unknown or hypothesized planets beyond Pluto. Eris is an actual, newly discovered dwarf planet, a little larger than Pluto but much farther away. By conflating these, some were claiming that NASA had found Nibiru or that Eris was going to fly past Earth in 2012.

Q: I was on the NASA home page and searched Planet Niburu. Come to find out there actually is a planet beyond Pluto and they are calling it Niburu. Some said Planet Niburu didn’t exist but now we know it does! There haven’t been many straight answers on this subject so I don’t really expect to get the total truth, but here I go. Is there ANY chance of a Niburu flyby in 2012? And if there is why don’t the public have a right to know so that we can prepare ourselves?

A: I’m sorry if the NASA web page confused you. I just checked, and there is no mention of Nibiru other than recent statements that it does not exist and is a hoax. The web site does include a 2005 news story on the discovery of one of the transneptunian dwarf planets, 2003UB313. UB313 was subsequently given the name Eris, and there is plenty of information about Eris on the web, including a good introduction in Wikipedia. But this has nothing to do with Nibiru. Nibiru is a hoax, linked to a religious cult, and having nothing to do with science.

Q: How can you call Nibiru a hoax when your own IRAS detected it and you issued a press release in 1982 which made it to eight major newspapers?

A: When looking into this sort of thing, you need to read past the first paragraph, since new data are always coming along in science. IRAS (the first infrared survey satellite, which flew more than 20 years ago) cataloged 350,000 infrared sources, and initially many of these were unidentified (which was the point, of course, of making such a survey). All of these observations have been followed up by subsequent studies with more powerful telescopes both on the ground and in space. The rumor about a “tenth planet” erupted in 1984 after a scientific paper was published in Astrophysical Journal Letters titled “Unidentified point sources in the IRAS minisurvey,” which discussed several infrared sources with “no counterparts.” But these “mystery objects” were later found to be distant galaxies. The bottom line is that Nibiru is a myth, with no basis whatever in fact. To an astronomer, persistent claims about a planet that is nearby but invisible are just plain silly.

Q: I have been reading the questions and answers about Nibiru. I am glad you say it does not exist. However Eris does exist and I see they were going to call it Xena . . . planet X. On this Website when you type in Nibiru Eris comes up and it clearly states it is the 10th planet. Will Eris do a flyby since it is considered a planet and the 10th one? Is Eris coming toward us? Could this even be possible that we would be thrown off our axis? Are Pluto and others really slightly of their normal gravitational paths because of this planet that is supposedly coming toward us? Why do they say time is speeding up because of the magnetic pulse this planet is creating? Is this true that there are only really 16 hours a day now because time is moving faster? Is that possible? Why do the days seem so much shorter? I am scared about this whole 2012 thing. Eris seems to be in the position that everyone says Nibiru is and the same size. Maybe we are asking the wrong question. Maybe we should be asking about Eris and not Nibiru. Thank you for your time as I am scared to death!

A: There is no factual basis for the many Nibiru stories. This Internet chatter originated from the claim by Nancy Lieder that she was warned about this planet by aliens from the star Zeta Reticuli. In the absence of real information, however, people speculate and embellish this fictional story. One such addition is to link Nibiru with “Planet X,” a term used for many years by astronomers to refer to any unknown planet that might exist beyond Pluto. Far from being a real object, this term indicates an unknown or undiscovered object (that is why it is called “X”). Another false link is with Eris, the largest of the dwarf planets recently found beyond Neptune, designated 2003 UB313 when it was discovered in 2003. Before Eris was given its formal name, its discoverer, Mike Brown of Caltech, informally referred to it as Xena, a word play on “Planet X.” The name Eris was officially adopted by the International Astronomical Union in 2006. However, this has nothing to do with Nibiru. Nibiru is supposed to be a large planet on a highly elliptical orbit with a period of 3,600 years, which comes onto the inner solar system and will disrupt Earth in 2003 (the original claim) or 2012 (the current claim). Eris is a dwarf planet (smaller than the Moon) with a period of 557 years, currently far beyond Neptune or Pluto at a distance of about 10 billion miles. Its orbit will never bring it into the inner solar system; the closest it will come, in about 2255, is 4 billion miles. Eris does not match the fictional object Nibiru in distance, orbit, size, or any other property, and it does not threaten Earth in any way. The other items you mention from the Internet are untrue. Neither Pluto nor any other transneptunian object is deviating from its normal path. Time is not speeding up, and the days are not shorter. You know as well as I do that there are still the usual 24 hours in the day, not 16! Please don’t be scared; the entire Nibiru story, as well as any concerns about Eris threatening Earth, are a hoax, nothing more.

Trying to Contain the Topic

At the beginning of February, I combined several similar questions in the hopes that I could lay this topic to rest and get back to writing about real science.

Q: Recent questions about Nibiru: (1) I have found a lot of stuff about a so called planet. Planet x or Nibiru. If anything they say [is] possible like revolving around the sun clockwise and it has been said that its orbit is way far out past Pluto. Also there are statements that it has a 3600-year orbit around the sun and that [it] is supposed to return in the near future. Is this possible at all? It sounds fishy to me, but there are supposed pics of it and a lot of scientist talk about it. I even wikipedia searched it. I would just like to find out some info please. (2) Nibiru does exist and I can prove it. Nibiru is in the old testament Exodus 6:4. and you are watching Nibiru from a lab on the south pole. also I have images from a telescope of Nibiru. and people from the southern hemisphere can see Nibiru in the daytime. is that proof enough for you? (3) many signs tell that something big is out there coming and why wouldn’t it be true about nibiru / planet x? why build a telescope at the south pole an photos and such with this redish dwarf star moving fast in 1983 it was 50 billion miles away and 10 years later it is alot closer is it hiding behind the sun i know you all dont want to start a world wide panic. (4) I read were you said that Nibiru is a hoax. My question to you is why would anyone let the american population know about such a catastrophy? Isnt it the governments job to keep the population at ease? (5) What is this a picture of? http://www.greatdreams.com/nibiru-possible.jpg It’s said to be Nibiru, but as you say Nibiru is a hoax. so what is this really a photo of?

A: I hope this is my last comment on the Nibiru hoax, but questions like the above five keep coming in. Most of the entries on the Internet about Nibiru are false. Wikipedia has it correct when they write that “Nibiru is a name in Sumerian, Babylonian astrology associated with the god Marduk, generally accepted as referring to the planet Jupiter.” The rest is a hoax, including all the “stuff” questioner #1 found on the Internet. Questioners #2 and #3 mention the astronomical observatory at the South Pole, but I assure you these astronomers are not looking at Nibiru. The Antarctic is a great place for infrared astronomical observations, and it also has the advantage that objects can be observed continuously without the interference of the day-night cycle. Questioners #3 and #4 seem to think that the government would hide information about Nibiru and the catastrophe coming in a few years, but I can’t imagine why. My experience is, in fact, that sometimes parts of the government do just the opposite, as in the frequent references to various terrorist threats. In any case, the job of NASA scientists is to discover and tell the truth! Finally, questioner #5 asks me to identify two pictures. I can only guess that these might be images of an expanding gas cloud (nebula) ejected by a star in its old age. They are obviously very distant, since we see stars in the foreground superposed on the nebula. [A sharp-eyed reader later identified these photos as an expanding gas shell around the star V838 Mon].

Questions Become Angry and Threatening

Having called Nibiru a hoax on a NASA Web site, I had opened myself to a growing series of abusive emails (which I did not answer). Here is a sample:

Q: I can’t believe This!, you still have the gall to lie to the hole world about planetX Nibiru, How dare you do that, yet you keep on calling youself a Senior Scientist, shame on you, people must keep on knocking hard on your door until you give up and come clean.

Q: Sorry but you say Nibiru is a Hoax? Doesnt Exist? So maybe The Sumerian people doesnt exist also! Nibiru does exists and its the new Planet discovered in 2005 size of Pluto. It is talked about centurys ago in Sumerian Civilization. Stone Plates with the planet were found! Its possible to say that this planet giant orbit passes between Sun and Earth and causes the Glaciar Eras to happen. I talk about the facts! Like science usually does! So how can you say its a hoax???

Q: I hope I can get an honest answer and not a lie. I would like to know more about this Nibiru thing. Not that your really going to tell me the truth here are you? I have been told that by May 2009 it will be seen by the average person is this true? I will not take kind to someone endangering my family because they want to keep a secret.

Q: The question isn’t why are you lieing to the people about the exsistance of Nibiru, the question is do you think you will be spared when it’s effects come to pass.

Q: Why are we (the people) not informed of a possible catastrophe, especially one of this magnitude to take into consideration. I really don’t expect the truth from you guys.

Q: So if you all are watching Eris and it’s trajectory, why can’t you tell us about how it’s going to come between the sun and the earth? Where is the info on your webpage of the true trajectory which will cause the perturbing of all our solar system heavenly bodies? If this is nothing to worry about, then why don’t you talk about its trajectory? Why don’t you have people partnering to watch it, track it and be actively talking about this huge new planet that is coming? Why are you so quiet about this new discovery? Your behavior is suspicious and your actions will be discovered soon so I would suggest a full disclosure.

Q: I know for a fact that Nibiru is a planet the Sumerians knew this. We discovered Pluto in 1930 but the Sumerians knew it existed in 4500 b.c. Voyager 2 made the first close-ups from Neptune and Uranus in 1986 and we saw how the planets looked like up close. The Sumerians in 4500 b.c. knew that already. How is it that there info is so accurate and Nasa with all this technology cannot find Nibiru? Is Nasa keeping this planet from us?

Q: Why do you continue to claim this is a hoax? what is it in 1983 the heavenly body that you discovered then covered up saying it was nothing? why is it that closer to 2012 we see increased volcanic activity, earthquakes, tsunamis, flooding, droughts, and much more? its not from global warming! this activity is happining on other planets as well.

Q: I think NASA is trying to cover up the up coming of planet X or Nibiru in year 2012. Is it because this world is over population and some of us need to die? Why is NASA being fishy about this?

Q: Why would you people rather die than warn people and prepare for this kind of thing?!

Q: Don’t play stupid with me because you are obvisly not going to answer my question with truth not like its your fault but the goverments and higher powers.

Q: I understand you don’t want to loose your job. So I know your answer about Nibiru. You, Nasa, the USA government and whoever else will deny till it will be undeniable. Mankind is going to disappear and nothing will change this truth. I hope you couldnt live with this lie over your shoulders anymore.

Q: Everybody knows that planet x and nibiru exist, when is NASA and the government going to come clean and stop bold face lying to the american people. People have a right to survive this calamity. No wonder everybody say’s NASA stands for never a straight answer!

The Questions Keep Coming

Following are a few of the questions from March and April, which I (perhaps foolishly) have continued to try to answer. These include some new twists, such as the claim that the Sun will be in the center of the Milky Way Galaxy in December 2012, and this is what will cause “pole shifts” and other cosmic catastrophes.

Q: Now if the Nibiru topic is a hoax, then what are the infrared images of the alleged Nibiru??? And i also heard that NASA saw it with IRAS and reported it and all that.. Why does NASA deny anything about it instead of telling the public so (if Nibiru is in fact a hoax) they dont take drastic measures such as my family was planning on doing. I need more proof that Nibiru is a hoax because the government and NASA are keeping to much from us for us to make full judgement on it. . . .

A: I really am sorry that you have taken the Nibiru hoax seriously, and that this hoax is causing you and your family distress. This Nibiru stuff is all pure fiction, without any core of fact or truth. Specifically (1) The are no infrared images of Nibiru—period. (2) IRAS (the Infrared Astronomy Satellite, which carried out a sky survey for 10 months in 1983) discovered many infrared sources, but none of them was Nibiru or Planet X or any other objects in the outer solar system. (3) NASA scientists tell the truth. There is no reason why we would not do so, and besides truth-telling is a fundamental value of scientific research. (4) It is unreasonable to ask us to prove that Nibiru is a hoax. Your questions should be to Nibiru proponents to prove to you that what they are saying is true, not for NASA to prove it is false. The burden of proof falls on those who make wild claims. Remember the often-quoted comment from Carl Sagan that extraordinary claims demand extraordinary levels of evidence if they are to be believed.

Q: I understand that you said nibiru is a hoax but why on this website http://www.detailshere.com/niburu.htm they have live picture of nibiru.

A: The website you sent me is pretty funny. For example, the statement that the Earth’s axis had tilted and the Sun had shifted from its correct place in the sky; anyone with eyes can see this is not true. Or the comment about building observatories at the south pole to observe Nibiru. There is no celestial configuration possible that could be seen only from the Antarctic and not from the whole southern hemisphere. And they ask why no observatories have been built near the North Pole. The last time I looked, the North Pole was in the middle of the Arctic Sea, not exactly the sort of place to build a telescope. I am also bemused by the claims that Nibiru has remained hidden behind the Sun for years. The impossibility of such an orbit has been clear since Johannes Kepler published his first two laws of planetary motions in 1609. Anyway, thanks for a good laugh.

Q: When most of the planets align in 2012 and planet earth is in the centre of the milky way, what will the effects of this be on planet earth?

A: There is no planet alignment in 2012 or any other time in the next several decades. As to the Earth being in the center of the Milky Way, I don’t know what this phrase means. If you are referring to the Milky Way Galaxy, we are rather far toward the edge of this spiral galaxy, some 30,000 light-years from the center.

Q: I was wondering what the conclusions were about the possibility of a polar shift, and if that happened what the effects would be to everyday living.

A: Quite a few people have been asking me about the danger of a polar shift, and I must confess that I don’t know what you mean by the term. “Polar shift” seems to have become a buzzword on websites that promote catastrophist ideas and various conspiracy theories, and so this phrase gets passed on from one blog to another without ever being defined. If this means some sudden change in the position of the pole (that is, the rotation axis of the Earth), then that is impossible. There is no point in speculating about the consequences of something that has never happened and never will. Before geologists discovered the role of plate tectonics (about 60 years ago), there was some speculation that a polar shift was involved in transforming the Antarctic from a warm to a cold climate, but now we know it was the Antarctic continent that moved, not the rotation pole. The very small and gradual changes that do take place in the position of the pole are responses of the Earth to changes in the distribution of mass on the surface, for example due to freezing or thawing of glaciers. The bottom line is that there is no possibility of a “polar shift” and no danger associated with one.

Q: How can you say that a pole shift is impossible? The geological record shows repeated reversals of the Earth’s magnetic field.

A: Thanks for pointing out an ambiguity concerning the term “pole shift”. As I wrote in my previous answer, everything I have seen predicting destruction from an alleged pole shift concerns the rotational pole of the Earth. There is no chance that this rotational pole will shift to a significant degree. The magnetic pole is different; it regularly shifts position by a small amount, and as you note, the polarity of the Earth’s magnetic pole reverses roughly once per million years (on average). This magnetic reversal appears to be generated internally and not to be influenced by any outside events. There is no indication that it will happen anytime soon, but more to the point, a magnetic reversal would not cause any of the horrible consequences that you find associated with “pole shift” on the catastrophist Internet sites.

Q: If the world was going to end would you tell us?

A: The short answer is “of course I would tell you.” Science is about discovering and communicating the truth about nature, not keeping secrets. But on a more basic level, I don’t understand questions that ask about a possible end of the world in 2012. This world has been peacefully going its way for 4.5 billion years, with life evolving for probably 4 billion years. Do you really imagine that after 4 billion years it is all going to end 4 years from now? And how could it possibly happen? There is nothing around that could destroy a planet. The worst damage that we could inflict on our ecosystem is probably associated with global warming and loss of habitat, which are already causing a mass extinction, but none of that threatens the future of the planet itself.

Weirder and Weirder

As I write this in June, questions keep coming in. In addition, nine out of ten of the “most popular” questions and answers on “Ask an Astrobiologist” are about Nibiru, not astrobiology. This experience is baffling on several fronts. While I hope that many people who read my replies are pleased to learn that the world is not about to end, I am surprised at so many angry responses. These come from people who seem to want the world to end in 2012, who are upset to be told that this catastrophe will not happen. I am also struck by their lack of perspective about time or space. For example, my correspondents seem to accept the claim that the magnetic influence of Nibiru is already causing a pole shift even though the object is invisible to astronomers. Some even accept that the tilt is already apparent, or even that the world is “turning upside down.” They also accept that we will be in the center of the Milky Way Galaxy, 30,000 light-years away, in 2012. The fact that none of this is being reported in newspapers or on television is simply accepted as evidence of a grand conspiracy. Do they ever ask themselves why governments are pursuing wars in Iraq and Afghanistan, worried about global warming, and conducting an energetic presidential election in the U.S. if they all know the world will end in four years? It has been a revelation to me to glimpse this underworld of conspiracy theories and doomsday predictions.

To conclude on a lighter note, the following recent questions are actually quite amusing:

Q: I have read about the things all about nibiru, and i was completely shocked from this matter, but for many years untill now as i gazed towards the sky during at night, i have noticed a huge star beyond us, I would like to ask is that eris? because the size has dramtically increased over the last couple of years?

Q: Recently there have been a good amount of scary stuff going around in the world. An earthquake and a cyclone. Not only that but it seems that the world is turning upside down.

Q: I am an experimental physicist. I am currently working on anti-gravity technology. I have recieved an infra-red reading of an object travelling into our solar system. This lab does not contain any astrophysicists but we believe this object (around 1.2 times the size of Jupiter) is the new planet Niribu (Planet X). As rumours here have circulated. Its orbit is highly eliptical and will pass into the inner-solar system. I would like to comfirm a couple of things for me. Is this accurate—Our facts are based on rumour, the scan is only a basic, find objects to test on scan. Does this object pose any danger to the Earth? Would any danger occur in a test of experimental technology to deviate the object from its current course? The generator we have created theoretically can move any object of any size, as mass should not affect the fields created.

Q: I hear that the beings who are on the Nibiru mother ship which houses smaller ships inside are coming to help the inhabitants of Earth to raise their polarity levels up so the plane would shift up to 4D. Have you heard about this? Please be honest. Theres a lot of information on YouTube that speaks about this. I always knew that another advanced lifeform was here and is working to get us ready for the shift. I would like for one of them to reveal theirselves on TV on CNN. Wouldn’t you?

I would particularly like to acknowledge Clarke’s contribution to my own field of understanding and protecting the Earth against cosmic impacts. I chaired the first scientific study of cosmic impact hazard, responding to a 1990 request from Congress to NASA. Our team proposed a “Spaceguard Survey” of near-Earth asteroids, and we called ourselves the Spaceguard Working Group. The name “Spaceguard” had been coined in Clarke’s novel Rendezvous with Rama, in which it described a future system to detect any incoming asteroids or comets in time to protect the Earth from a catastrophic impact. Clarke graciously endorsed our use of the term, which has become synonymous with asteroid surveys. He supported our efforts to initiate this survey and was pleased to have his name associated with such a worthy endeavor.

Partly inspired by the new attention to the impact hazard, Clarke wrote a novel in 1994 on this theme: Hammer of God. The plot concerns efforts to deflect a large comet on a collision course with Earth. This novel was acquired by a Hollywood studio and became the basis for the 1998 film Deep Impact, although Clarke himself did not write the script. Deep Impact was an intelligent film, realistically depicting the impact threat and the ways we might respond if faced with such a calamity. Unfortunately it was released at the same time as the blockbuster film Armageddon, which made no effort toward accuracy, either scientific or political. If your memory of these two impact films is dominated by the antics of Bruce Willis in Armageddon, I recommend you watch Deep Impact again. Also well worth reading is Clarke’s New York Times op-ed of August 14, 1994, entitled “Killer Comets Are Out There. Now What?” for an articulate defense of the importance of the Spaceguard Survey and future efforts to develop a defense against cosmic impacts. (The New York Times reprinted this 1994 op-ed on March 23, 2008).

All of us who have been entertained and inspired by Sir Arthur Clarke mourn his passing.

In this new remembrance of Carl Sagan, who died ten years ago, a noted planetary scientist and colleague (and former student of Sagan) recalls Sagan’s immense contributions to planetary research, the public understanding of science, and the skeptical movement.

Carl Sagan was the world’s best-known scientist in the late twentieth century, serving as our guide to the planets during the golden age of solar system exploration. He was both a visionary and a committed defender of rational scientific thinking. Sagan died on December 20, 1996, while only 62, and he has been greatly missed in the decade since. In addition to my own knowledge and insights about his scientific and skeptical contributions, I have made extensive use of the two excellent narrative biographies by William Poundstone (1999) and Keay Davidson (1999). Poundstone is stronger on Sagan’s science, Davidson on his personal history. Neither, however, emphasizes his role as a skeptic.

Sagan was propelled on his academic and public careers by enormous talent, good luck, and an intensely focused drive to succeed. His lifelong quest was to understand the universe, especially our planetary system, and to communicate the thrill of scientific discovery to others. A natural teacher, he loved to explain things and never made a questioner feel stupid for asking. Although Sagan had broad intellectual interests, his pursuit of his career left little time for other activities: he did not play golf or follow sports, take up cooking or photography, sing or play a musical instrument, or join a church or synagogue. His first two wives complained that he devoted insufficient time to his marriages or his children (Davidson 1999). He focused on his career goals, and the world was enriched thereby.

Many scientists would like to be able to communicate with the public about their discoveries. However, few become adept at explaining technical subjects in terms that are readily understood by the lay public. Even fewer are willing to take the time to answer journalists’ questions patiently, to sit still for application of makeup for television appearances, or to return reporters’ calls promptly even when they interrupt a meal or a lab experiment. They might like to be great communicators, but they lack the skills and the commitment. They also recognize that academic rewards generally come to the best researchers, with limited honor associated with excellence in teaching and even less for public outreach. Sagan was different. He recognized his talents as a teacher and popularizer and decided to make such outreach a major aspect of his career.

Born in 1934, Sagan grew up in a working-class Jewish neighborhood of New York and attended urban public schools in New York and New Jersey. The University of Chicago provided him scholarship support when he entered in 1951, and he continued there for graduate work, receiving his doctorate in astronomy in 1960. After two years as a postdoctoral fellow in biology at Berkeley and Stanford, he joined the Harvard College astronomy faculty as Assistant Professor. Denied tenure at Harvard, Sagan moved to Cornell University in 1968, serving as David Duncan Professor of Astronomy and Director of the Laboratory for Planetary studies until his death in 1996.

Research

Although best known to the public as a popularizer, Sagan first distinguished himself as a research scientist. His accomplishments in research made it much easier for his academic peers to accept him as a spokesperson for science. Sagan loved the research process, especially when it was combined with the exploration of new worlds. As he often noted, only one generation was privileged to grow up when the planets and their moons were little more than dim points of light in the night sky, and to see them emerge as unique worlds with their own geological and perhaps even biological history. Sagan helped define two new disciplines: planetary science and exobiology. As a leading consultant to NASA, he also helped chart the exploration of the solar system by spacecraft.

With training in both astronomy and biology, Sagan brought a unique breadth to the emerging new fields of planetary science and exobiology. At the time he received his doctorate, his thesis advisor Gerard Kuiper recognized that “Some persons work best in specializing on a major program in the laboratory; others are best in liaison between sciences. Dr. Sagan belongs in the latter group” (in Davidson 1999).

Sagan was an “idea person” and a master of intuitive physical arguments and “back of the envelope” calculations. He usually left the details to others, and most of his published papers were collaborations. Much of this work was done with students, many of whom went on to become leaders themselves in planetary science. On much of his later work, including the famous TTAPS paper on nuclear winter (more on this later), his name appears last among the listed authors. Throughout the 1970s and into the 1980s, he also edited the foremost professional journal in planetary science, Icarus.

Sagan’s most important early research dealt with the atmosphere of Venus. Discoveries in radio astronomy made when he was in graduate school first suggested that this planet had a very hot surface, in contrast to previous speculation that the climate of Venus was more Earth-like. Part of Sagan’s thesis consisted of the first computed greenhouse model for the atmosphere, in which the high infrared opacity of carbon dioxide and water vapor produced a surface temperature hundreds of degrees higher than that of an airless planet. Over the decade of the 1960s he improved these models, working primarily with his former student James Pollack, to develop and refine what remains to this day our basic understanding of the atmosphere of Venus.

Mars was another planet that interested Sagan, and with Pollack he modeled the atmosphere and developed the idea, later verified by the Mariner 9 and Viking spacecraft, that quasi-seasonal changes observed on the surface were the result of wind-blown dust. He also wrote a series of papers on Jupiter, focused on atmospheric organic chemistry.

From childhood, Sagan had been inspired by the mystery of the origin and distribution of life. This passion led him to study biology and develop collaborations with leading biologists such as Stanley Miller, and Nobel laureates Joshua Lederberg and George Muller. Early in his career, he received more encouragement from these biologists than from astronomers, many of whom considered planetary studies to lie on the fringes of respectable science, and exobiology to be beyond the pale. A number of his early publications were in exobiology, and at various times he speculated about life not only on Mars, but also on Venus, Jupiter, and even the Moon. In spite of his increasing role as a scientific skeptic, he permitted himself to indulge in this broad speculation, so long as his ideas remained within the realm of possibility. Sagan was also one of the founders of international interest in SETI, the microwave search for extraterrestrial intelligence, although he himself did not conduct any searches.

NASA valued Sagan’s contributions to the spacecraft exploration of the planets during its “Golden Age” (roughly 1960—1990). He was a member of science teams selected for the Mariner 2, Mariner 9, Viking, Voyager, and Galileo missions, among others. With his quick mind and breadth of vision, he was always a welcome contributor to planning sessions and the “quick look” interpretation that followed the first receipt of spacecraft data. His former student Clark Chapman wrote in 1977: “A man of vivid imagination, he keeps alive a wide variety of conceptions of planetary environments. By suggesting often outlandish alternatives and challenging traditionalists to disprove them, he has inspired doubts about many accepted theories. Sagan’s role is essential for healthy science because a bandwagon effect frequently leads to premature consensus among scientists before equally plausible alternatives have even been thought of, let alone rationally rejected.”

Sagan’s own excitement with the process of scientific discovery is captured in the following quote (Sagan 1973): “Even today, there are moments when what I do seems to me like an improbable, if unusually pleasant dream: to be involved in the exploration of Venus, Mars, Jupiter, and Saturn; to try to duplicate the steps that led to the origin of life on an Earth very different from the one we know; to land instruments on Mars to search there for life; and perhaps to be engaged in a serious effort to communicate with other intelligent beings, if such there be, out there in the dark of the night sky.”

Popularizer and Skeptic

At the same time he was building up an enviable bibliography (which grew to 250 pages by the end of his life) and a record of successful students, Sagan also established a growing reputation as a popularizer of science. His boyish good looks, resonant voice, and ability to explain scientific concepts in ways that lay persons and students could understand made him a popular teacher and public lecturer. He won teaching awards at Harvard and Cornell, and even in the busiest times of his life he tried to keep his hand in undergraduate teaching.

In 1966 he first achieved some modest national attention with his book (with the Russian astronomer I. S. Shklovskii) Intelligent Life in the Universe. The following year, Sagan wrote an upbeat article on the potential of life on the planets for National Geographic, and he made a few brief TV appearances. Already it was apparent to some that Sagan sought a broader role than that of academic researcher, a concern that probably contributed to denial of tenure by Harvard University in 1967. Students loved him, but some colleagues bristled at what they perceived as self-aggrandizement and pandering to the public. Unlike Harvard, Cornell University was looking for faculty with a potential for stardom, and they provided Sagan an endowed chair and the solid academic springboard he needed for his future rise to fame and fortune.

Throughout his career, Sagan devoted himself to the quest to improve public understanding of the nature of science. He wanted every citizen to have a “baloney detector” as defense against sham in commerce and politics as well as science. He felt that it was the duty of scientists to face these issues squarely and publicly. The Cosmic Connection (1973), which includes extensive discussions of extraterrestrial life as well as more conventional astronomy and planetary science, even explores the UFO phenomenon and the writings of pseudo-cosmologist Immanuel Velikovsky. However, Sagan opposed tactics that demeaned pseudoscientific beliefs or attacked religion, refusing (for example) to sign a statement against astrology because of its authoritative tone.

His interest in popular misconceptions about science led him to organize two public symposia on fringe-science topics at meetings of the American Association for the Advancement of Science (AAAS). Both arguably concerned real scientific issues, not cases of fraud or religious extremism.

The first AAAS symposium, in 1969, dealt with the reality of UFOs. Like many scientists of his generation, in high school Sagan had been attracted to the idea that UFOs might be visiting spacecraft. At the AAAS, J. Allen Hynek and James McDonald defended UFO studies while Sagan, Donald Menzel, and Lester Grinspoon attacked this position. The proponents on both sides of the issue were scientists, although they took very different approaches to the interpretation of the anecdotal reports of UFO sightings. (The subject of alien abductions or direct contact with extraterrestrials, which has since become so common, was not an issue at that time; the AAAS symposium focused on the interpretation of moving lights in the sky and anomalous radar signals.)

UFO proponents argued that even though there was no individual sighting in which one could make a compelling case for extraterrestrial spacecraft, the sheer volume of reports justified continuing examination and study. In contrast, Sagan emphasized the unreliability of witnesses, the absence of physical evidence of UFOs, and alternative explanations including hallucination and self-delusion. He noted that “there are no cases that are simultaneously very reliable (reported independently by a large number of witnesses) and very exotic (not explicable in terms of reasonably postulated phenomena),” and he applied a skeptical standard that is often associated with his name: that extraordinary claims require extraordinary levels of evidence or proof.

The 1974 AAAS symposium, on the work of Velikovsky, was riskier, since Velikovsky himself was invited to speak under AAAS sponsorship, something he claimed as a vindication. While Sagan promoted the symposium, it was actually organized by historian Owen Gingerich and astronomers Ivan King and Donald Goldsmith. Velikovsky’s thesis of global catastrophes caused by numerous planetary encounters within historical times was scientifically indefensible but had attracted a wide popular following. Unlike the UFO symposium, there were no scientists to defend these ideas, published in his 1950 book Worlds in Collision (dismissed by Sagan [1973] as a “speculative romance”). Rather, the 77-year-old Velikovsky confronted his debunkers personally.

Keay Davidson (1999) describes the symposium as part apology to Velikovsky for previous slights from astronomers, and part an effort to reassure the public of science’s basic fair-mindedness. The confrontation of the patriarchal Velikovsky and his young, brash critic was a clash of egos on both sides. Sagan aimed his remarks, published in extended form in Scientists Confront Velikovsky (Goldsmith 1977), primarily at the public and science journalists. By most accounts he was the hands-down winner. Many people credit this debate as the beginning of the end for the Velikovsky cult, which is today reduced to a handful of obscure cranks.

However, Sagan’s role earned him the bitter enmity of Velikovsky supporters. His greatest sin was his lack of respect for the old man, who steadfastly refused to accept any modification of his then quarter-century-old views. Sagan’s critique of Worlds in Collision was also castigated by Velikovsky followers for its failure to address all of his claims, and for some slipshod calculations that were never corrected in Sagan’s published remarks. This symposium has been extensively analyzed (e.g., Bauer 1984), and it still raises unanswered questions about the most effective ways to counter pseudoscientists. Similar scenarios are replayed today by scientists who debate creationists and defenders of intelligent design. I sometimes ask myself if Sagan would have ventured into this lion’s den, and if so how a debate between him and, say, creationist Duane Gish, would have played out.

Both AAAS symposia were widely covered by the media and contributed to a growing public recognition. A further boost came in 1973 with the publication of The Cosmic Connection, described in Science (Hartmann 1974) as “thirty-nine genuine, vintage Sagan dinner conversations.” This description was more accurate than the reviewer may have realized. This book, like all of Sagan’s, was dictated. Creating his books and popular articles this way, Sagan simultaneously developed his unique speaking and writing styles. At his lectures, listeners were impressed by his carefully crafted sentences, and by the way his talks (delivered without notes) seemed to be so well organized. Dictation turned out to be the perfect way for Sagan to organize his thoughts and develop his prose style simultaneously. It allowed him to “write” while traveling or walking on the beach, and it never necessitated his learning to type. It also allowed him to derive multiple value from the same material, typically delivering his message in various lectures, writing it for a magazine article (for such outlets as Parade), and using it as the basis for a chapter in one of his books.

The Cosmic Connection helped open the door to a medium that Sagan seemed destined for: television. In November 1973, he was invited to appear on the popular Tonight Show with Johnny Carson (himself a skeptic). Handsome, articulate, informal in manner, yet enthusiastically discussing real science (and often bringing the latest photos from NASA missions like Viking and Voyager), he captivated both the audience and the host. Over the following thirteen years, Sagan appeared on The Tonight Show twenty-six times. No matter how pressing his other business, he was always willing to take a break and fly to Hollywood for Carson. He considered it “the biggest classroom in history.”

In January 1974, Time did a cover story on life in the universe, in which it called Sagan “the prime advocate and perennial gadfly for planetary exploration.” A few weeks later Sagan published an article in TV Guide, the largest circulation magazine in the United States. Sagan was suddenly hot, receiving media attention normally reserved for a select few Nobel Prize winners. In August 1976, Newsweek put his smiling face on its cover, a rare accolade for any scientist. Their thumbnail sketch stated: “At 42, Carl Sagan has become the leading spokesman and salesman for the new science of exobiology, the search for extraterrestrial life. Lobbying in Washington, appearing on television talk shows, and teaching at Cornell, he is building fresh support for the space program and fulfilling his own fantasies of finding life out there.” Two years later, he received the ultimate tribute for a science writer, winning the 1978 Pulitzer Prize for general nonfiction for his book about the human brain, The Dragons of Eden.

Sagan was a founding member of the Committee for Scientific Investigation of Claims of the Paranormal. CSICOP originated in 1976 in part to direct attention to egregious media exploitation of supposed paranormal wonders. (He was always supportive of CSICOP and the Skeptical Inquirer, and served as keynote speaker at two well-attended CSICOP conferences, Pasadena in 1987, Seattle in 1994, each of which led to a major article in SI: “The Burden of Skepticism,” Fall 1987, and “Wonder and Skepticism,” January/February 1995.) Sagan’s own contributions focused less on critiques of the media and more on creating news, skillfully using the media to inform and entertain about science. He preferred the positive approach, talking about what was correct rather than exposing errors in others.

Showman of Science

In the later 1970s, between the Viking mission to Mars and the anticipated Voyager encounters with Jupiter, Sagan decided to test the capacity of television to bring science to a mass audience. In partnership with engineer and entrepreneur Gentry Lee, a Viking colleague, he formed Carl Sagan Enterprises and began marketing a television series modeled on Jacob Bronowski’s Ascent of Man. They developed a script, raised several million dollars in support, and hired Bronowski’s director, Adrian Malone. At the same time Sagan fell rapturously in love with Ann Druyan, with whom he worked closely for the rest of his life. He and Annie moved to Los Angeles, and production at KCET Public Television started in 1977 on the 13-hour series called Cosmos.

Sagan with colleague Toby Owen at JPL in 1976, examining recent Viking orbiter photos of Mars. Sagan and Owen played key roles in deciding on the landing sites for the Viking spacecraft.

His commitment to Cosmos finally eclipsed Sagan’s academic roles. His classes were canceled, and several graduate students who had come to Cornell to work with him chose other advisors instead. Colleagues complained, and there was an effort to force his laboratory out of the Cornell Space Science Building. In Los Angeles, clashes of will between Sagan and Malone almost derailed the entire Cosmos effort. Cosmos aired in September 1980, accompanied by a promotional effort that exceeded anything seen before in public television. Most reviews were enthusiastic, and suddenly Sagan became a celebrity. The series won the Peabody Award, and eventually more than 400 million people saw Cosmos in dozens of countries around the world. The accompanying book, also called Cosmos, was on the New York Times best seller list for seventy weeks and made him wealthy as well as famous.

In October 1980, Sagan appeared on the cover of Time, shown wading in the “cosmic ocean.” Time described him as the “Showman of Science” and the “prince of popularizers.” They wrote: “Sagan sends out an exuberant message: science is not only vital for humanity’s future well being, but it is rousing good fun as well. Watching with wonder—and no doubt a little envy—the whirling star named Sagan, some of his colleagues feel that he has stepped beyond the bounds of science. They complain that he is driven by ego. They also say that he tends to overstate his case, often fails to give proper credit to other scientists for their work, and blurs the line between fact and speculation. But they probably represent a minority view. Most scientists, increasingly sensitive to the need for public support and understanding of science, appreciate what Sagan has become: America’s most effective salesman of science.”

Sagan with Ann Druyan in 1980 during the filming of Cosmos.

Sagan moved back to Cornell after Cosmos, but he could not return to the anonymity of the campus. People stopped him on the street and interrupted his meals in restaurants to tell him how much they liked Cosmos or to ask for his autograph. He mused to me at the time how strangers felt comfortable approaching him, since after all he had been in their living rooms (on TV). He also received crank calls and death threats, requiring police patrols of his home and prompting the university to remove his name from his office door and from the Space Science Building directory.

Fame also had its rewards. He bought a spectacular home modeled on an Egyptian temple, perched on the edge of one of Ithaca’s wooded gorges, and hired a personal staff. He received an unprecedented advance from Simon & Shuster of $2 million for a science fiction novel to be called Contact, before he had written a word. Contact was published in 1985, and later made into a successful film starring Jodie Foster.

Sagan’s popularity did me a service at about this time. Driving across West Texas, I was stopped for speeding. As the police officer started to write a ticket, he asked what I did for a living. When I mentioned that I had been Carl Sagan’s student, he put away his citation book and launched into enthusiastic praise for Carl and, by implication, for his friends and students.

Journalist Joel Achenbach, in Captured by Aliens (1999), noted that once Sagan achieved superstardom with Cosmos, he became the public lightning rod for both the science and the pseudoscience of extraterrestrial life. As the “keeper of the gates” who effectively defined the border between science and pseudoscience, he was actively courted by many fringe figures who sought in his blessing a legitimization of their interests or beliefs. As an example, Achenbach reported this interview with Richard Hoagland, the popularizer of the “Face on Mars.” Hoagland explained that in a public meeting in 1985, Sagan commented that those planning NASA missions to Mars should be open to discovering the unexpected. According to Hoagland, when Sagan made these remarks, he briefly made direct eye-contact with Hoagland, who was in the audience. In the weird world of pseudoscience, Sagan’s innocent comment was interpreted as a coded message encouraging Hoagland to pursue his advocacy of an artificial origin for the Face—which he continues to this day, in spite of all the evidence to the contrary. (See some of Sagan’s thoughts on the Hoagland/Mars Face matter in “Carl Sagan Takes Questions: More from his ‘Wonder and Skepticism’ CSICOP 1994 Keynote,” Skeptical Inquirer, July/August 2005.)

Sagan’s role is especially interesting because he himself was accused of straying beyond the limits of proper science in his pursuit of evidence for life on other planets and his defense of SETI. As Achenbach argues, it was precisely because of his apparent open-minded attitude toward fringe topics that many on the fringe became so bitter when Sagan turned against them.

Making a Better World

Sagan at Cornell in 1974 with three former students (L to R): David Morrison, Joseph Veverka, and James Pollack.

Sagan’s rise to celebrity occurred simultaneously with Ronald Reagan’s escalation of arms spending and cold war rhetoric. He told colleagues that he intended to return to the life of a professor, but he also felt he should use his new wealth and power to accomplish objectives of more global scope. As an early opponent of Reagan’s Space Defense Initiative (SDI) or “Star Wars,” he was able to rally vocal objections from the academic community that questioned both the technical basis for SDI and its potential destabilizing effect on the nuclear balance.

In 1982, an even more compelling opportunity presented itself, thanks to research involving two of his former students, Jim Pollack and Brian Toon (both at NASA Ames Research Center). With colleagues Rich Turco and Tom Ackerman, they were studying the influence of dust and atmospheric aerosols on global climate, working to understand the effects of martian dust storms and of the dust cloud that enveloped Earth following the asteroid impact that caused the extinction of the dinosaurs. In 1982, they had realized that smoke, especially from petrochemical fires, would have a much greater effect on global climate than naturally occurring dust. In fact, it appeared that the smoke from as few as 100 burning cities, when lofted into the stratosphere, could lead to severe global cooling (nuclear winter).

Turco and Toon flew to Ithaca in late 1982 to enlist Sagan’s aid, for both the technical aspects of the research and as a means to overcome NASA objections based on the political implications of this work. This collaboration generated the TTAPS paper (named for the first initials of the authors, but with obvious symbolism) on nuclear winter published in Science in late 1983. The TTAPS authors concluded that even a less-than-full-scale nuclear exchange, especially if it were directed against cities, could cause global cooling and collapse of agriculture. The massive loss of life would hit victor, vanquished, or non-combatant nations alike.

Sagan used his prestige to argue that these new findings rendered nuclear war obsolete and undermined the concept of massive nuclear retaliation. The debate was international, including within the USSR, where it stimulated a rethinking of nuclear war-fighting strategies. But the pro-nuclear forces in the United States counterattacked vigorously, vilifying Sagan personally in the process. The National Review called nuclear winter “a fraud” and titled one cover story “Flat-Earth Sagan Falls off the End of the World.”

Edward Teller, who at seventy-three was probably the second best known scientist in America, debated Sagan on nuclear winter before a special convocation of Congress. Sagan also led a delegation to meet with Pope John Paul II, who subsequently issued a papal statement against the build-up of nuclear arsenals. Many people credit this theory, and its advocacy by Sagan, as influential in the move toward nuclear disarmament and the end of the cold war.

Sagan oscillated between roles as scientist and political advocate. In this period, while attending a meeting of the imaging science team for the Galileo spacecraft, Sagan apologized to his teammates for his inability to commit more time to this mission, saying he was “putting most of my energy into saving the world from nuclear holocaust.” Most team members agreed that this effort should indeed have a higher priority for Sagan than planning imaging sequences for the moons of Jupiter.

In parallel with its escalation of the arms race, the Reagan administration cut back drastically on NASA’s program of planetary exploration. In 1981 they threatened to close down the highly successful Voyager 2 spacecraft before its Uranus and Neptune encounters and to turn the Jet Propulsion Laboratory into a defense contractor lab. After the space shuttle Challenger accident in 1986, the momentum seemed to have left NASA, just when Sagan was advocating an accelerated exploration program in his books and lectures. At the same time the USSR, under the influence of Mikhail Gorbachev’s reforms, seemed more open to international collaboration.

Sagan saw an opportunity to achieve two goals of noble dimension. By working together on missions to Mars, the US and the USSR could build confidence and gain experience that would ultimately defuse the cold war and permit cooperation in other areas. By pooling their resources, these two space-faring nations could accomplish together what neither could afford alone—extending human presence into the solar system—and simultaneously ensure peace on Earth.

Sagan formed a close working relationship with Roald Sagdeev, the director of the Space Research Institute in Moscow, and together they opened up the Soviet planetary exploration program, with unprecedented live reporting of the Soviet flybys of Comet Halley in 1986. In Russia, he associated with Soviet cosmonauts and government officials as well as scientists. For a few years, under his leadership, anything seemed possible. Then the USSR disintegrated, and many of its space scientists found themselves unemployed. With the failure of Russia’s last three planetary missions (all destined for Mars), both the motivation and the capability of Russia to partner in exploration of the solar system evaporated.

Disappointments

By the time of the final Voyager encounter with Neptune in 1989, it was apparent that Sagan’s campaign to promote human expansion to Mars was doomed. His Russian friend Sagdeev was emigrating to the United States and marrying (of all people) Dwight Eisenhower’s granddaughter. And after a decade of budget cuts, NASA seemed unable to summon the resources even to maintain a modest program of robotic space exploration. The high hopes of the Viking and Voyager era were gone. In a 1989 lecture at JPL, Sagan could not conceal his frustration and disappointment—the first time I had seen him unable to summon an optimistic perspective. However, worse personal blows were about to fall.

In the autumn of 1990, Sagan made his most serious scientific blunder. Threatened with military opposition to its invasion of Kuwait, Iraq threatened to set fire to the nation’s oil wells. Sagan became concerned that the quantity of petrochemical smoke generated by these oil-field fires could generate a small-scale nuclear winter, endangering crops across Asia and threatening world food production. Of his four TTAPS co-authors, only Turco supported this hypothesis; Pollack, Toon, and Ackerman could not see how sufficient smoke could get into the stratosphere. However, Sagan went public with dire predictions. While he kept his predictions conditional, saying only that we could not show that massive oil-field fires would not have major climatological consequences (a “double negative” logic that he used frequently), his doomsday warning was widely reported. The oil fields were torched in January 1991, blackening the sky over most of Kuwait and disrupting the coastal ecosystem, but there were no climatic effects, even on a local scale. Sagan was widely criticized, and the episode had the further effect of undermining the credibility of the entire nuclear winter scenario.

The next year Sagan was nominated for membership in the National Academy of Sciences. Academy membership requires distinguished research scholarship, but that is rarely sufficient to ensure membership. Considerable weight is also given to public service, as well as more political factors such as where a nominee works and whom he or she knows. Most colleagues agreed that Sagan’s research record was more than adequate (Shermer 1999), and that his additional journal editorship, government service, and contributions to public understanding of science should have ensured his election. But Sagan was blackballed in the first voting round, requiring a full debate and vote by the Academy membership. In the final vote he barely received 50 percent yes votes, far short of the two-thirds majority required for election to membership.

Two years later, the National Academy awarded Sagan its prestigious Public Welfare Medal, perhaps in partial compensation for his earlier rejection. The damage was done, however: not only a stinging personal blow, but also an attack on his credibility as a spokesperson for science. For all his accomplishments—or perhaps because of some of them—influential members of the academic “old boys” network never accepted him.

Other problems multiplied. In 1993 the NASA SETI program, which he had defended on critical occasions in the past, was abruptly terminated by Congress. His book on nuclear winter, written with Turco, sold only a few thousand copies; no one cared much any more about issues of nuclear war. Perhaps worst of all, a book that he and Annie put a great deal of themselves into, Shadows of Forgotten Ancestors, did not receive the enthusiastic welcome they expected. Although some reviewers consider it one of Sagan’s best works, it was not a best seller. No longer a media star, Sagan was slipping from public consciousness.

Sagan with the author at a planetary science meeting in 1983.

A Candle in the Dark

Sagan’s most important contributions in his final years were in the struggle against pseudoscience. Throughout the last decade of the millennium, this scourge of public irrationality grew, as astrology, alien abductions, alternative medicine, and any number of other New Age and “millennial” fads and cults gained in popularity. Sagan fought back, and after the death of his friend Isaac Asimov, his was the voice most often heard in defense of scientific reason in the United States.

His most influential platform was provided by the weekly newspaper-supplement magazine Parade, one of the two most widely read publications in America. His column appeared there regularly for more than a decade, providing a unique opportunity for outreach and education. He discussed the latest discoveries in science, debunked the purveyors of flimflam, and also delved into sensitive topics of public concern such as abortion and animal rights. His articles in Parade provided the basis for many chapters in his final three books, Pale Blue Dot, The Demon-Haunted World, and Billions and Billions.

The Demon-Haunted World, subtitled Science as a Candle in the Dark, was a passionate defense of science against pseudoscience and irrationality, as illustrated in the following quotes. “It is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring [that may be]. . . . Superstition and pseudoscience keep getting in the way [of understanding nature], providing easy answers, dodging skeptical scrutiny, casually pressing our awe buttons and cheapening the experience, making us routine and comfortable practitioners as well as victims of credulity. . . . [Pseudoscience] ripples with gullibility. . . . The tenants of skepticism do not require an advanced degree to master, as most successful used car buyers demonstrate. The whole idea of democratic application of skepticism is that everyone should have the essential tools to effectively and constructively evaluate claims to knowledge. . . . But the tools of skepticism are generally unavailable to the citizens of our society. . . .Those who have something to sell, those who wish to influence public opinion, those in power, a skeptic might suggest, have a vested interest in discouraging skepticism” (Sagan 1995).

While vigorously advocating the concepts of scientific skepticism, Sagan also raised questions about strategy. He wrote that “The chief difficulty I see in the skeptical movement is in its polarization: Us vs. Them—the sense that we [skeptics] have a monopoly on the truth; that those other people who believe all these stupid doctrines are morons.” He was especially troubled by anti-religious attitudes. While not a believer himself, Sagan had constructive interactions with religious leaders, including the Pope and the Dalai Lama. He wrote “There is no necessary conflict between science and religion. On one level, they share similar and consonant goals, and each needs the other.”

Although more demanding and hence less popular than his books about astronomy and planetary exploration, The Demon-Haunted World is arguably his most mature and valuable publication. Expressing his concerns about the irrationalism that pervades modern society, he wrote: “I know that the consequences of scientific illiteracy are far more dangerous in our time than in any time that has come before. It’s perilous and foolhardy for the average citizen to remain ignorant about global warming, say, or ozone depletion, air pollution, toxic and radioactive wastes, topsoil erosion, tropical deforestation, exponential population growth. . . . How can we affect national policy—or even make intelligent decisions in our own lives—if we don’t grasp the underlying issues? . . . Plainly there is no way back. Like it or not, we are stuck with science. We had better make the best of it. When we finally come to terms with it and fully recognize its beauty and power, we will find, in spiritual as well as in practical matters, that we have made a bargain strongly in our favor.”

Sagan’s example has contributed to increasing efforts by scientists to reach out to the press and the public. For the first time in the 1980s, such professional organizations as the American Astronomical Society and the American Geophysical Union appointed full-time press officers and began sponsoring press conferences at their annual meetings. NASA missions also undertook to identify and encourage project scientists to speak with the press, both informally and as official NASA spokespersons. In the late 1990s this extended to welcoming commercial HDTV crews into high-level NASA meetings and spacecraft encounters. Breaking with tradition, the space agency was now anxious to show the human side of scientific exploration. In the 1960s, Sagan was almost alone in his work with the press, but such activity had become relatively common among space scientists two decades later. None, however, has approached Sagan’s level of charisma or public name recognition.

Cornell’s President Frank Rhodes, speaking at Sagan’s sixtieth birthday celebration, summarized his impact: “I want to salute Carl Sagan . . . as the embodiment of everything that is best in academic life . . . in scholarship, teaching, and service. . . . Carl is an inspiring example of the engaged, global citizen . . . . [He is] a master of synthesis, and he has used that skill to engage us as a society in some of the biggest issues of our time. . . . With the conscience of a humanist and the consummate skill of the scientist, he addresses the needs of the society in which we live, and we are the richer for it” (Terzian and Bilson 1997).

References

• Achenbach, Joel. 1999. Captured by Aliens: The Search for Life and Truth in a Very Large Universe. New York: Simon and Shuster.
• Bauer, Henry. 1984. Beyond Velikovsky: The History of a Public Controversy. Urbana, Illinois: University of Illinois Press.
• Chapman, Clark. 1977. The Inner Planets. New York: Scribner.
• Davidson, Keay. 1999. Carl Sagan: A Life. New York: Wiley.
• Hartmann, William. 1974. Review of The Cosmic Connection. Science 184: 663—664.
• Morrison, David. 1999. Sagan and skepticism: Review of two Sagan biographies. Skeptic 17, (4): 29—31.
• Poundstone, William. 1999. Carl Sagan: A Life in the Cosmos. New York: Henry Holt.
• Sagan, Carl. 1973. The Cosmic Connection: An Extraterrestrial Perspective. New York: Doubleday. (Reissued 2000 as Carl Sagan’s Cosmic Connection: An Extraterrestrial Perspective. Cambridge: Cambridge University Press.)
• —. 1987. The burden of skepticism. Skeptical Inquirer 12(1): 38—46.
• —. 1995. Wonder and skepticism. Skeptical Inquirer 19(1): 24—30.
• —. 1995. The Demon-Haunted World: Science as a Candle in the Dark. New York: Random House.
• Shermer, Michael. 1999. The measure of a life: Carl Sagan and the science of biography. Skeptic 17(4): 32—39.
• Terzian, Yervant, and Elizabeth Bilson, eds. 1997. Carl Sagan’s Universe, Cambridge: Cambridge University Press.

Today astrobiology has developed into an international multidisciplinary field, bringing together biologists, chemists, astronomers, geologists, and planetary scientists to seek common ground. There are two major professional journals in astrobiology, international meetings, several nascent professional societies, a NASA Astrobiology Institute (where I work), and an explosion of college courses and books on this topic. It is within this broader context that we should examine SETI programs and their scientific underpinnings.

Studies of life on our planet continue to broaden our understanding of the robustness of life, and its ability to survive and even thrive in seemingly extreme environments, ranging from boiling hot springs to Arctic sea-ice to the cooling water of nuclear reactors. But while life may be widespread, detecting it on other worlds is challenging. Within our solar system, we may need to return samples to Earth for detailed study that might reveal unambiguous signatures of past or present life. For planets around other stars, astronomical techniques are all we have. The problem here is to understand what global biomarkers (such as oxygen in an atmosphere) can be relied upon, and how we can develop the new instruments to make the required measurements. SETI presents us with an alternative approach to biomarkers. While the occurrence of a technological civilization is probably rare even on living worlds, the detection of a radio or optical signal from such a civilization would provide unambiguous evidence of life.

Peter Schenkel’s article “SETI Requires a Skeptical Reappraisal” mostly lacks the modern astrobiology perspective. His target is high expectations of the success of SETI based largely on philosophical positions that go back to Giordano Bruno. In fact, much of his article seems to be aimed at refuting his own past optimistic positions, making his reappraisal a personal statement of reduced expectations. Probably the truth about current ideas on SETI lies between these optimistic and pessimistic extremes.

One area in which I believe Schenkel is too negative is the matter of the prevalence of exoplanets-planets circling other stars. It has been common in evaluations of the Drake equation to set this number at between 10 percent and 100 percent, based until recently on little hard information, since no exoplanetary systems had been discovered. All this has changed in the past decade, with more than 150 exoplanets known today. Initial results were confusing and perhaps disheartening for SETI supporters, since the systems being discovered were dominated by giant planets very close to their suns. These “hot Jupiters” are incompatible with the presence of Earth-like planets. But these strange (to us) configurations are actually found in only about 10 percent of solar type stars. Recent improvements in detection technology are now revealing systems with giant planets in jovian-like orbits, which leave open the possibility of terrestrial planets like our own. Today these Earth-like planets are undetectable, but within three years the NASA Kepler observatory should be able to find analogues of Earth. Thus the new results, while inconclusive on the prevalence of Earths, are actually encouraging. Earth-like planets may be common in the universe, and we should soon know!

The “rare Earth” hypothesis is also used by Schenkel as an argument against the common presence of inhabited planets. He correctly lists several unusual features of Earth that seem to have been favorable to the evolution of advanced life. The exact duplication of such a situation in another planetary system is indeed rare. But are these elements of our past history really required? I do not think we know enough about the origin and evolution of life to define the range of conditions that are conducive to life and intelligence. Earth is rare, but it does not necessarily follow that inhabited planets are rare.

His note that it required “more than 96 percent” (I think he meant 99 percent) of the age of Earth for higher intelligence to evolve illustrates an interesting logical error. We always look at the past from our present perspective. I read Schenkel’s article only today, which represents less than one trillionth of the age of the Earth, but that really does not say anything about the probability of this article having been written and sent to me by the editor of SI. Besides, there are probably many Earth-like planets with up to twice the age of our solar system.

Is SETI likely to succeed in our lifetimes? I do not know. I hope so, of course, but I cannot assign a probability to such near-term success. I think the situation demands skepticism but not pessimism. I think that Schenkel would agree with this perspective.

There are two well-known SETI-related conclusions of which we can be confident, however. If we succeed, any civilization we detect will almost surely be far in advance of our own, and the message itself may be indecipherable. We should not, therefore, look to SETI for easy solutions to our current challenges on Earth. The second conclusion is that, while we may not succeed if we search, we are assured of failure if we do not search.

Public opinion polls tell us that we are losing the battle to explain the nature of evolution and the central role that evolutionary concepts play in modern science. Tens of millions of Americans scoff at evolution and try to protect their children from what they consider to be a pernicious concept.

Given the overwhelming scientific support for evolution, we must be doing something wrong in discussing this issue with the public. There are several ways in which scientists and educators might enhance their effectiveness in this debate. The problems relate to framing the issues, or rather, allowing the opponents of evolution to frame them. Framing involves the selective use of language or context totrigger responses, either support or opposition. We see it in the often deceptive titles of legislation, such as a “clear skies act” or “forest renewal act” or, on the other side, a “death tax.” “Pro-choice” or “pro-life” advocates are always careful to frame their position with the proper emotion-charged terms. (The subject is artfully described in George Lakoff’s book Don’t Think of an Elephant.)

As a prime example, we doom our communications efforts with many nonscientists by defending the “theory of evolution.” Theory is quite simply the wrong word. Polls indicate that three quarters of Americans agreed that “evolution is commonly referred to as the theory of evolution because it has not yet been proven scientifically.” Those who advocate adding “only a theory” disclaimers in textbooks know that to call evolution a is sufficient to undermine its acceptance.

Channeling the discussion into a debate over the “theory of evolution” is an example of framing. Since the great majority of Americans understand the word theory to imply uncertainty and vagueness, the name itself predisposes the answer. It is as if a criminal defendant were described by the judge and other court officials as “the murderer.” Not many juries would want to let a known murderer free, no matter how the evidence was presented. The one who frames the debate often wins.

Yet many proponents of evolution seem content to argue about the “theory of evolution” and its educational role. As scientists, they were taught that a scientific theory is a systematic set of principles that has been shown to fit the facts, and has stood up against attempts to prove it false. A theory is thus the highest level of understanding, synthesizing a wide variety of observations and experiments. But that is not what the word theory means to 99 percent of Americans, including many scientists and educators when they are outside the classroom.

Dictionaries have noted the changing definition of this word. Older dictionaries give preference to the scientific definition and consider the use of theory to refer to a guess or hunch to be a form of slang. Today, the slang meaning prevails, and a theory is a belief, something taken to be true without proof, an assumption, a suggestion, a hypothesis. Similarly, theoretical is used as a synonym for tentative, an idea that has not been tested with observations.

How do we really use the term in everyday language? A theory is a hunch that a detective comes up with in a murder mystery. It is one of several competing ideas, none of them proved. Fringe theories and conspiracy theories are crazy ideas that are out of the mainstream. New medicines or changes in the tax laws may be good in theory but don’t work in practice. Among some scientists, theorists are thought to lack solid grounding in the facts (see the accompanying sidebar).

What about scientific usage? We don’t hear much anymore about the Theory of Gravitation, or the Atomic Theory of Matter, or the Theory of Plate Tectonics. These phrases have a vaguely antique flavor. Gravitation and atoms and plate tectonics are accepted as legitimate subjects that don’t need the preface “Theory of.” The only two areas where “Theory of” remains in common use are Theory of Relativity and Theory of Evolution. Relativity is associated with Einstein, a genius whose work was abstract and unintelligible to laypeople. I doubt if most people realize that the principles of relativity have been tested, or that relativity has practical implications, for example in calculating the interplanetary trajectories of spacecraft. Judge for yourselves what this association implies for “Theory of Evolution.”

There is another usage that should be mentioned: theory as a discipline, such as organization theory, color theory, economic theory, music theory, etc. These phrases imply the existence of a knowledge base or conceptual framework, and their names are given to university courses or areas of specialization. In science there are chaos theory, cosmological theory, information theory, and—yes—evolutionary theory (as used in the title of Steve Gould’s last book). This usage is, however, rarely discussed in arguments about “only a theory.”

If we accept the framing that calls this topic the theory of evolution, we face a dilemma. Some people just ignore the problem and concentrate on presenting the facts of evolution. They may believe that these facts and their implications are self-evident. But the human brain does not always work that way. We have seen recent examples. The majority of voters who supported the 2004 re-election of George W. Bush told pollsters that they believed that Saddam Hussein had weapons of mass destruction and that he had been behind the September 11 terrorist attacks, despite countless news stories to the contrary. Many people believe that airplanes are more dangerous than cars, no matter what risk statistics are presented. Even after well-conducted trials showed that herbal medicines such as echinacea are ineffective, public sales have remained strong.

Alternatively, many scientists and educators recognize the public misunderstanding of the scientific term theory and try to explain this to the audience. In her excellent book Evolution vs. Creationism, Eugenie Scott devotes much of the first chapter to the scientific meaning of the terms theory, hypothesis, falsification, etc. However, few members of a nonscientific audience with concerns about teaching evolution to their children are ready to accept that this word, whose meaning they know perfectly well, has in fact an almost opposite definition in science. Thus before asking the audience to consider that their opinions about evolution might be wrong, we start by asking them to accept a contrary definition for a familiar word. Anyone who teaches knows how hard it is for students to unlearn things they already know and believe. So why do we accept this wholly unnecessary burden when discussing evolution? No wonder those who frame evolution as a theory often win.

We should be discussing simply evolution, the same way we might discuss plate tectonics or genetics or any other branch of science. To debate the “theory of evolution” is a trap. It is letting our opponents frame the discussion to their benefit. Once we stop defending the theory of evolution, we are also free to criticize “only a theory” disclaimers in textbooks without apology or diversionary explanations.

The Either/Or Fallacy

The concept of framing has other implications for the creation-evolution debate. One that we are all familiar with is the effort to portray this as a choice between two models—godless evolution versus divinely inspired creationism. In a two-model formulation, any perceived difficulty with evolution becomes support for creationism. We should not accept this framing of the conflict. Actually, I would think that today it would be obvious that there are at least three models on the table: evolution, the young-earth creationism of biblical literalists, and the more sophisticated concept of Intelligent Design (ID), which accepts the age of the universe and the change in Earth’s biota over time. It is a tribute to the discipline of the anti-evolution camp that they have avoided most public debates between the biblical literalists and ID. But we are free to exploit this split and to ask which alternative is proposed to be taught alongside evolution in science classes.

Most opponents of evolution in the schools are Christian fundamentalists, and many of them believe that evolution is a moral issue, a struggle between the forces of good and evil. Obviously proponents of evolution do not see it this way. What we want is a level playing field where we can present the facts. But as noted above, facts often lose out in a confrontation with deeply held beliefs.

To achieve a level playing field, we should avoid debating evolution in a religious context. Specifically, we should not speak on these issues in a church other than our own. In an unfamiliar church speaking to an audience of like-minded opponents of evolution, all the cards are stacked against us—not because there is anything antireligious about evolution, but because the audience believes there is. This situation also creates a temptation to debate religion itself, such as arguing about the “true” message of the first book of Genesis or contrasting the beliefs of Roman Catholics and fundamentalist Protestants. This is not likely to be a winning strategy for the scientist, who is again a victim of framing.

An Issue of Values

Many antievolutionists base their opposition not on scientific issues, but on their belief that evolution threatens their value system, specifically their family values. I don’t see why we should not face this issue directly. Family values are not the monopoly of the creationist advocates. Most in these audiences will share a common interest in the education of their children, which is a fundamental American family value.

If I were speaking to an audience of parents, I would stress that evolution is central to many sciences, and that one cannot be a scientist without understanding it. I would note that students who don’t understand evolution will have trouble getting into the best colleges. I would comment on the great number of scientists and engineers being graduated in “competitor” countries like China, and note that American students are not top scorers in international science tests. We can make a persuasive and nonpartisan case that the future of the nation depends on its scientific and technical literacy. Relatively few Americans will reject such arguments and state a preference for ignorance. Teaching evolution is part of a bigger issue of the competitiveness and economic well being of the nation (and of the state and local community). This is a real issue of values, for our children and their futures. And it is an issue that might appeal to lay members of school boards and textbook selection committees.

Health is another value issue. Medical research is supported by Americans across a wide political spectrum. How many people understand the role of evolution in the development of new medical treatments? Or the place played by genetics in creating new drugs? There is no more dramatic (or scary) example of evolution than the emergence of drug-resistant pathogens, as well as recent diseases such as AIDS. Newspaper stories about threatened pandemics due to mutations in avian flu or other emerging viruses can only be understood in an evolutionary context. Suppressing the study of evolution cuts off future opportunities to improve public health. Surely this values argument has wide appeal.

Beyond Biology

We also suffer when we accept that evolution should be debated purely in terms of biology and biology courses. In the present American public school system, these courses are already watered-down so that evolution is likely to be mentioned in only or one or two chapters or discussed in only one study unit of a biology course. It is easy to belittle a subject that seems so marginal. We should reframe this issue in terms of crosscutting ideas that affect all science. The audience should know that evolution and the concept of deep time are essential to geology and astronomy and genetics and pharmacology as well as high-school biology. It is also an opportunity to tell an audience how many people in this country are working in evolution-related jobs. If the audience comes from a traditional conservative religious background, they may have no idea that evolution is widely accepted among scientists and medical professionals and that it contributes to the livelihood of many Americans.

Many conservative Americans support competition and believe that free-market economic conditions are essential to national success. Most of them would be shocked to know that this philosophy has traditionally been known as social or economic Darwinism. Perhaps we should note that Darwinian natural selection is in many ways nature’s equivalent to free-market competition. The other side of this argument addresses the belief that evolution leads to socialism and communism. Perhaps it is worth noting that Stalin’s support for the anti-Darwinian biologist Trofim Lysenko set back Soviet agriculture for a generation and contributed to the starvation of millions of Russians.

Finally, we can reframe the issue in terms that do not immediately offend a conservative religious audience. The context in which most opponents fear and reject evolution is that of human origins. The scientific story of the evolution of our human ancestors is fascinating, but it also provokes the strongest resistance. My own interests, as an astrobiologist, are in microbial evolution, which is a less threatening subject. I remember a young teacher coming up to me after a lecture and saying how amazed she was that I had talked for an hour about evolution and the history of life without mentioning primate evolution or human origins. I am not suggesting that we ignore the fascinating story of homonid evolution, but I bet that there are many people who would be more receptive to evolutionary concepts if we refrained from an in-your-face challenge to their convictions about human origins or the nature of the human soul.

Another topic that is controversial is the origin of life. Creationists love to confuse origins with evolution. They frequently use criticisms of, for example, the relevance of the Miller-Urey experiment to undercut the entire concept of biological evolution. Let’s not be sidetracked into the problems of the origin of life. While a great deal of research has been done to define the conditions under which life began on Earth and to understand basic biochemistry, the actual process by which living things emerged is not understood by science. I believe we can and should admit this mystery. There may be many people who will open their minds to the ideas of evolution as long as we don’t claim that science has all the answers, especially about the ultimate origin of life and the meaning of being human. These topics can be explored later, when we have overcome initial emotional resistance to any form of evolution.

Above all, I hope that we can frame the evolution-creationist debate in ways that open our audience to the exciting ideas and accomplishments of science. When appropriate, we should be happy to defend teaching evolution in the context of family values and economic advantage as well as pure science. There is no reason to make this a debate about religion; we are almost sure to lose such a confrontation. But we must also understand where our audience is coming from and find ways to present the science in a non-confrontational and accessible way.

SI on Evolution and ID

Here is a list of some other Skeptical Inquirer articles on Intelligent Design and creationism.

• Charles Sullivan and Cameron McPherson Smith, “Getting the Monkey off Darwin’s Back: Four Common Myths about Evolution,” May/June 2005
• Dennis R. Trumble, “One Longsome Argument,” March/April 2005
• Robert Camp, “‘Teach the Controversy’: An Intelligently Designed Ruse,” September/October 2004
• Bruce and Frances Martin, “Neither Intelligent nor Designed,” November/December 2003
• Mark Perakh, “A Presentation without Arguments: Dembski Disappoints,” November/ December 2002
• Mark A. Wilson, “‘Geology Confronts Creationism’: An Undergraduate Science Curriculum,” January/February 2002
• Randy Moore, “Educational Malpractice: Why Do So Many Biology Teachers Endorse Creationism?” November/December 2001
• Taner Edis, “Darwin in Mind: ‘Intelligent Design’ Meets Artificial Intelligence,” March/April 2001
• David Roche, “A Bit Confused: Creationism and Information Theory,” March/April 2001
• Martin Gardner, “Intelligent Design and Phillip Johnson,” November/December 1997 (our earliest article on ID) News Articles/Editorials:
• “Time for Science to Go on the Offense,” July/August 2005
• “AAAS Board Urges Opposing ‘Intelligent Design’ Theory in Science Classes,” March/April 2003
• “Botanical Society of America’s Statement on Evolution,” November/December 2003
• “Bogus Poll of Scientists Latest Twist in ID/Creationists Fight against Science Standards,” November/December 2003
• “American Association of Physics Teachers Statement on the Teaching of Evolution and Cosmology,” January/February 2000
• “Science Trumps Creationism in New Mexico,” January/February 2000

News releases and media reporting on asteroid impact-related science frequently exaggerate the uniqueness and significance of new research. We should be skeptical of all claims of scientific revolutions.

Many observers of the science press have noted an increasing tendency for both news releases and printed stories to exaggerate the uniqueness and significance of new research. The writer of a news release does this to increase the probability that the media will cover the story, and the media reporter will go along with this hyperbole or perhaps expand it further to get the story approved for publication by editors or other gatekeepers.

The field of impacts (and impact hazards) is not immune to these trends. In my NASA-supported Web page http://impact.arc.nasa.gov, I try to apply a filter to reduce the noise level in media reports, which would otherwise overwhelm much of the real science.

This is not intended as a general criticism of science reporting. There are many excellent science journalists who understand the issues and provide well-reasoned discussions of context for news stories. Overall, the reporting by science journalists of impact-related stories has been excellent. But a hyperbolic headline added without their knowledge can sometimes catch even the best writers.

Background on Asteroids and Impacts

In his excellent book Mysteries of Terra Firma (Free Press, 2001), geologist James Powell discusses three revolutions in our understanding of Earth history. The first, responding primarily to the discovery of radioactivity at the end of the nineteenth century, was the concept of deep time-measurement of the age of Earth and dating of the primary geological and evolutionary events in its history. The second revolution dealt with the discovery of plate tectonics, first suggested (as “continental drift”) but subsequently rejected early in the twentieth century. Plate tectonics was accepted only in the 1960s (when a wide range of strong new evidence was obtained) and has become the fundamental theory for understanding the dynamics and history of the Earth’s crust. The third revolution was the space-age recognition of the role of cosmic impacts on geology and evolution.

Scientists are still exploring many implications of this third revolution. Space exploration missions to other worlds and careful scrutiny of impact landforms on Earth have revealed that cratering is a universal process in the solar system. The pioneering work by Walter Alvarez and colleagues on the end-Cretaceous mass extinction further showed that cosmic impacts can have profound influences on the evolution of life. Whether other mass extinctions are also due to impacts remains an open question.

My own interest in impacts includes the contemporary danger from asteroids colliding with Earth. Although the probabilities are low, a devastating impact capable of killing hundreds of millions of people could happen at any time. The NASA Spaceguard program, which seeks to find any threatening asteroid in time to mitigate the impact (preferably by deflecting the asteroid away from Earth), is one response to a growing awareness of the impact problem.

Did the KT Impact Cause the Extinction of the Dinosaurs?

The KT (Cretaceous/Tertiary, 65 million years ago) extinction is by now an old story, but sometimes the news media still report dramatically opposed conclusions as if a major debate existed to this day. Certainly the issue was contentious when impact extinction was first proposed by the Alvarez team twenty-five years ago, but a scientific consensus had emerged by the early 1990s. This progress of the Alvarez theory, increasingly supported by new evidence (such as the discovery of the Chicxulub Crater in Mexico), has been chronicled in several excellent books, such as Night Comes to the Cretaceous by James Powell, T. Rex and the Crater of Doom by Walter Alvarez, The End of the Dinosaurs by Charles Frankel, and When Life Nearly Died by Michael Benton.

In spite of the scientific consensus, there was substantial media coverage in 2004 of alternative hypotheses of dinosaur extinction. Major stories have arisen from the work of paleontologist Gerta Keller at Princeton, who has been challenging the impact theory for more than two decades. Recently she has decided that impacts may indeed be implicated, but probably not the Chicxulub impact (just off the coast of the Yucatan peninsula, the impact most earth scientists think is primarily responsible). One hypothesis she has suggested is that while the 100-million-megaton energy Chicxulub impact was insufficient to kill the dinosaurs, a smaller impact 300,000 years later may have done so. Princeton University frequently issues news releases on her work, and sometimes the publicity gets out of hand, with bold headlines such as “KT Mass Extinction Debate Wide Open and in Full Swing,” “The Space Rock Was Framed: Asteroid Cleared in Dinosaurs’ Death,” and “Asteroid Couldn't Have Wiped Out Dinos.”

One characteristic of media hype is to suggest that all science dealing with the KT extinction is about dinosaurs. Dinosaurs are popular. But dinosaur fossils, which are relatively rare, do not define the mass extinction boundary, which is precisely marked in the marine fossil record by changes in single-celled protists, as well as by the global layer of extraterrestrial material and shocked quartz from the impact.

On the other hand, some scientists discuss the dinosaur extinction without reference to the simultaneous global mass extinction in which more than half of all biological families were lost. This attitude is reflected in the remark by paleontologist David Penny that “We agree completely with the geophysicists that an extraterrestrial impact marks the end of the Cretaceous. But after twenty-five years [scientists] have still not provided a single piece of evidence that this was the primary reason for the decline of the dinosaurs.” [1]

Most scientists consider it to be exceedingly unlikely that the dinosaur extinction was unrelated to the global KT event. In addition to the coincidence in time and increasing evidence that the dinosaur extinction was abrupt, we think we understand how the Chicxulub impact killed large land animals by a combination of brief global firestorm followed by months of cold. Neglecting this relationship is one fatal flaw in this year’s widely reported hypothesis that dinosaurs went extinct because of disparity in the numbers of males and females born. Perhaps in this case the publicity was stimulated by the word sex, as in the Washington Times headline “Why Dinosaurs Died-It’s All about Sex.”

An Impact-caused Extinction 250 Million Years Ago?

Was the end-Permian mass extinction caused by an impact? No one knows, even though the PT event (Permian/Triassic, 252.6 million years ago, a newly published, more precise date for the prime extinction) was the greatest of all mass extinctions, with more than 90 percent of families becoming extinct. The past year has seen several new scientific results, many associated with claims and counter-claims concerning the submarine Bedout impact (or non-impact) structure that might (or might not) be the “smoking gun” crater. Also widely reported have been evidence of extraterrestrial material (but not iridium or shocked quartz, so far) at the PT boundary, and recent indications that the PT extinction may have been two sharp events separated by several million years.

I have no quarrel with the media coverage of these issues, except where news releases claim that the question has been definitively solved. There is no consensus concerning the cause of the PT extinction, and hence every reason to follow the debates as they happen. For example, I will be interested in results from a blind test for evidence of an impact that is being conducted by a team of scientists using new samples from China, where an excellent cross- section of PT rocks is accessible.

Meteorites and Fires

Meteorites do not cause fires. Yet it is common to find news reports that a bright meteor fell and started a fire. Often the existence of a fire is quoted as evidence that the meteor struck the ground (thus making it a meteorite).

In 2003, the old idea that both the Great Chicago Fire of 1871 and another conflagration more than a hundred miles north in Wisconsin were started by hot stones falling from the sky was revived. This coincidence seems striking, with two of the most destructive fires in U.S. history happening at the same time-but the coincidence might also be related to extreme dryness and high winds across the upper Midwest.

In the cases where we have been able to estimate the surface temperature of just-fallen meteorites (such as where they land on snow or ice), the data indicate that they are cool. Nor should this be surprising: the violent heating of the stone’s surface by atmospheric friction lasts only a few seconds, followed by several minutes of free-fall through the cold stratosphere. I follow the rule of thumb that if a meteor or meteorite is reported to have started a fire, the claim is probably mistaken. These are “meteorwrongs,” not meteorites.

The Recent Impact Rate

A common assertion in the tabloid press and on some Web sites is that we are at great risk from impacts, because impacts happen much more frequently than the scientists claim. Usually the argument is related to supposed evidence for recent large impacts.

One report (from The Guardian, on August 19, 2004) concerned huge craters under the Antarctic ice sheet said to be caused by an asteroid as big as the one that wiped out the dinosaurs, but striking about 780,000 years ago. The newspaper reported that an asteroid measuring three to seven miles across broke up in the atmosphere with five large pieces creating multiple craters over an area measuring 1,300 by 2,400 miles. Supposedly this impact caused a reversal in Earth’s magnetic field (a highly suspect claim) but little other damage. Obviously the description of this event is inconsistent with what is known about cosmic impacts, yet this “discovery” was reported seriously.

The “Sirente crater,” a lake near Abruzzi, Italy, has also been widely speculated to be an impact from the Roman period. If this were true, Sirente would be one of the most recent craters on Earth, falling right next door to the capital of the Roman Empire. However, no meteoritic material has yet been recovered from the lake. In 2004, an article in Tumbling Stone magazine suggests that this is an anthropogenic feature and not the result of an impact.

The Web site of Astronomy magazine published a report in October 2004 on identification of a field of meteorites and impact craters near Lake Chiemsee in southeastern Bavaria, Germany. This crater field, which falls within an ellipse 58 by 27 km, is said to hold at least eighty-one impact craters ranging from 3 to 370 meters in size. The authors, using historical and archeological evidence, conclude that an asteroid or comet fragment exploded above southeastern Germany in the Celtic-Roman period, probably around 200 b.c. They estimate that the projectile had a diameter of about 1 km. Since the authors are primarily amateur scientists and their work has not been published in a refereed journal, it is difficult for me to judge these conclusions, in terms of either the identification of impact craters or their probable date of formation. Another report, discussed below, suggests that there are many very dark, unseen comets that constitute a previously unrecognized threat.

In assessing the reliability of such stories, we should note that even one of these recent mega-impacts is unexpected from known impact rates, which are based on both astronomical observations and the long-term cratering history of Earth and Moon. (These impact rates might be off by a factor of two, but certainly not by a factor of ten or more.) For example, the Lake Chiemsee impactor is claimed to have been about 1 km in diameter and to have struck within the past 2,500 years, whereas on average an asteroid or comet this large hits Earth only once in about 500,000 years. While any one impact might be true (as a statistical fluke), it is hard to believe that several of these stories are correct. I remain skeptical.

Super-dark “Stealth” Comets

A new report in Monthly Notices of the Royal Astronomical Society by W.M. Napier, J.T. Wickramasinghe, and N.C. Wickramasinghe is titled “Extreme albedo comets and the impact hazard.” Based on a dynamical argument, they conclude that there should be more than 1,000 times more Halley-type comets than are actually observed. They therefore suggest that the comets become invisible, and that the impactor population is dominated by bodies too dark to be seen with current astronomical surveys.

One should be skeptical of a theoretical result that has no data to support it. One should be even more skeptical if it seems inconsistent with the data we do have, resolved (in this case) only by postulating a new class of “invisible” comets. But further, the idea that our astronomical surveys might miss huge numbers of such “stealth” objects is largely beside the point. We know about the low comet cratering rates from the dearth of small craters on Jupiter’s Galilean satellites, especially Europa. From this perspective it seems clear that there is not a large population of stealth comets to worry us.

Proposed Rain of Mini-comets

In the late 1980s, the proposal of a tremendous flux of tiny comets (each no bigger than a bus) was widely discussed in the science media. The discoverer was a well-respected space scientist from the University of Iowa, Lou Frank, who was attempting to interpret very small, transient dark patches in NASA spacecraft images of Earth’s atmosphere. Frank hit upon the idea that these dark spots were due to bursts of water vapor liberated in the upper atmosphere by disintegrating small comets, a hypothesis that he advocated at meetings of the American Geophysical Union, in published papers, and directly to many science journalists.

In spite of the excellent reputation of their advocate and invocation of NASA satellite data, an intense rain of such mini-comets was quickly recognized by most scientists as inconsistent with a wide range of other observations. The numbers of impactors proposed by Frank were a million times higher than the known flux of objects with their proposed mass. They would have to be so black that they were invisible to telescopes. Since their atmospheric impacts were also not being seen as meteors or flashes of light, they must also carry little energy. (The absence of a flash was later confirmed when data were released from sensitive surveillance satellites that constantly scan Earth from above.) They also evidently did not make craters when they struck the Moon. Finally, the amount of water vapor they would dump in the upper atmosphere was inconsistent with the known dry conditions in the stratosphere.

Although many scientists assumed that the dark spots were just noise in the spacecraft detector, they were unable to work with the raw data to verify this speculation. The media story persisted, aided by NASA news releases supporting the mini-comets. While they shook their heads in wonderment, few of Frank’s colleagues wanted to challenge him personally. His advocacy of mini-comets became an obsession-he even wrote a book called The Big Splash to market his ideas directly to the public. There seemed to be no polite way to make the story go away. One scientist tried, however, to counter with humor, when he proposed that the mini-comets be called Louis A. Frank Objects, or LAFOs.

Impact News in Great Britain

Based on the large sampling of press reports from both sides of the Atlantic collected by anthropologist Benny Peiser of Liverpool John Moores University, there seem to be significant differences in the press treatment of impact science stories between the United States and the United Kingdom. Many British science reporters like to play such stories for their humorous possibilities, as opposed to the straight science reporting that is standard in America. Ridiculing the “boffins” seems to be a popular way to treat scientific controversy. Another approach is to start off a story in a hyperbolic vein, only tempering the initial overstatements several paragraphs down. For example, an opening assertion might be made that an asteroid is on a collision course with Earth, but a few paragraphs later it is revealed the the probability of the impact is only one in 100,000. My impression is that the British reading public does not take this very seriously, and that their news reporting in general is intended to be more entertaining. A problem can occur, however, when such stories are picked up in other countries, where this tongue-in-cheek tone might be taken seriously. Let the reader beware.

Space science research dealing with impacts often makes a good story, especially when it is controversial. The public is likely to find science more interesting if they realize that research is carried out by real people working in a competitive environment. The controversy is very real in some cases, such as finding the cause (or causes) of the great PT mass extinction. In other cases, such as the KT mass extinction and the contemporary rate of impacts on Earth, a consensus exists based on multiple lines of evidence. While there are still many media-worthy stories, we should be skeptical of reports that the consensus has been overthrown by a single new result.

As Carl Sagan often said, “extraordinary claims require extraordinary evidence.” A similar admonition might be that before revolutionary theories are widely publicized, they need to be given a reality check. This is best done by the scientists deciding whether to issue a news release. But if the scientists are not self-policing, the burden falls upon the journalists to filter the signal from the noise, or upon the skeptical attitude of the reader.

Notes:

1. This quote is from a perceptive article ("In Extinction Debate, Dinosaurs and Science Writers are the Losers”) by Rob Britt at Space.com, 14 October 2004; see here.

A scientific consensus agrees that cosmic impacts have played a major role in Earth history and that they continue to pose a significant threat today. But there is a tremendous difference in the estimated dangers, stretching up to, or even over, the line that separates legitimate science from pseudoscience. Ten recent trade books are reviewed that span a broad range in interpretations.

As the millennium approaches, the media are playing up asteroid and comet impacts. Ten popular-level books were published in 1995 and 1996 dealing with the dangers of cosmic impacts, and now we are seeing a spate of television and movie productions, both factual and fictional, that describe the impact threat. It is easy to dismiss all this as media hype and millennial madness, but it would be a mistake to do so. While some books and films may be motivated by a desire to milk public credulity for a quick buck, most are serious efforts to inform the public about a real danger that is recognized by the scientific community. In this article, I summarize the background for the recent interest in impact catastrophes and then provide a comparative review of the current trade books that deal with this topic.

Background

Most scientists first thought about the role of impacts in Earth history in response to the now-famous paper published in Science in 1981 by Luis and Walter Alvarez and their colleagues, suggesting that an impact sixty-five million years ago produced the mass extinction that terminated the Cretaceous era. What was new in this paper was not the fact that Earth was struck by cosmic debris, but the idea that even relatively modest impacts might have a catastrophic effect on the environment. That Earth is subject to impacts is obvious from an examination of the cratered surface of our companion in space, the Moon. Planetary probes, beginning in 1964 with Mariner 4, have demonstrated that impact cratering is a universal process in the solar system. A heavy bombardment occurred early in planetary history, but it did not end then; a lower-level “rain of rocks” continues today, as comets and asteroids occasionally intersect the orbits of the planets. Those that come close and can pose a danger to Earth are collectively called Near-Earth Objects, or NEOs. On average, Earth should still expect to be struck by a fifteen-kilometer NEO every hundred million years or so. But the Alvarez paper and the research it stimulated also show that such impacts generate global-scale wildfires and dust storms, and thus are capable of killing most life forms and profoundly influencing the course of biological evolution. Impacts are the ultimate environmental disasters, more important than volcanic eruptions or other more familiar events in shaping the history of life on the planet.

Fortunately for us, impacts large enough to produce mass extinctions are rare, taking place at average intervals of tens of millions of years. However, there is a spectrum of comet and asteroid sizes, with many more small impacts than large ones. Based on what we know today, impacts much larger than the Cretaceous-Tertiary (K-T) event are possible in the future (although very improbable). And impacts smaller than the K-T event — say by objects one kilometer or a few kilometers in diameter — occur much more frequently. The planet is struck by a one-kilometer asteroid or comet at average intervals of about 100,000 years.

Another important aspect of these impacts is that they are, as far as we know, randomly distributed in time. The chances are equal that a big one could hit in 1997 or in 2248 or in any given year in the far future. Further, although a few teams of astronomers have been searching for NEOs, the census of these objects is far from complete. For instance, of the roughly two thousand kilometer-scale asteroids that are expected in Earth-crossing orbits, fewer than two hundred have actually been found. We are confident that Earth will not be struck in the foreseeable future by any of the known objects, but we can say nothing about the 90 percent that are not yet discovered. It is because we have not yet carried out a comprehensive search that we must speak in terms of probabilities. In reality, this is not a game of chance. There either is or is not an NEO out there aimed to hit us next year or in the next century. But we don't know about it yet.

Finally, we should realize that only a small fraction of the space around Earth is being monitored today and that the most probable warning for a kilometer-scale impact is zero — the first we would likely know of a strike is when we feel the ground shake and watch the fireball rising above the horizon. While several national and international observing programs have been proposed to accelerate the discovery of threatening objects, so far no government funds have been spent to deal with large-scale searches or any other efforts to mitigate the impact threat. There has been much talk, but little action beyond the efforts of a few individuals in the scientific and military communities.

Current Issues

Most of the books and TV specials deal broadly with the issues described above, including graphic descriptions of the destructive potential of impacts of various sizes and impact energies. The catastrophic climate changes that caused the death of the dinosaurs and other species at the end of the Cretaceous era are fascinating to scientists and laypersons alike. Another common element is the description of the 1994 collision of some twenty-three fragments of Comet Shoemaker-Levy 9 with Jupiter. This remarkable event, observed by hundreds of telescopes on Earth and in space, provided direct data on the nature and consequences of cosmic impacts. But a number of questions arise when we discuss the contemporary impact danger and consider whether — and how — to protect ourselves against future catastrophes. There is a considerable divergence among scientists in how such issues are framed and discussed, and an even wider disparity on the way these issues are presented to the public.

Let us begin with what I call the “standard paradigm” — that of random impacts on Earth by small comets and asteroids. This is the consensus view of most scientists, and it is reflected in two NASA reports to the U.S. Congress, the Spaceguard Survey Report of 1992 and the follow-up report in 1995 inspired by public interest in the collision of Shoemaker-Levy 9 with Jupiter. As the principal author of the Spaceguard Survey Report and a member of the follow-up working group (chaired by Gene Shoemaker), I identify with this consensus position.

The standard paradigm uses the cratering history of the Moon and other evidence to deduce the average historical rate of impacts on Earth by objects of different sizes or impact energies. It then assesses the destructive potential of impacts of different energies on Earth today in terms of probable casualties, noting in particular the existence of a threshold at about one million megatons of energy (corresponding to a two-kilometer asteroid) at which the global climate is severely affected and everyone is at risk, independent of proximity to the impact. One conclusion of such studies is that the statistical risk is greatest for impacts near the global threshold, amounting to an average risk of death for each individual on Earth of nearly one in a million per year, comparable to the risk of other more frequent (but less catastrophic) events such as earthquakes, severe storms, and volcanic eruptions. It is also noted that, unlike other natural disasters, impacts can be avoided entirely by deflecting an incoming object, if several years warning time is available.

Although most people agree that the greatest risk is posed by objects two kilometers or larger in diameter, others focus their attention on smaller impactors, especially those in the 200- to 500-meter range. When impacts of this size occur in the ocean, they produce tsunamis capable of inundating large stretches of coastline. Although the average risk for inhabitants of the planet is less from tsunamis than from the global catas-trophes caused by larger impacts, the risk for persons living on shorelines may be greater. This fact, together with the higher frequency of smaller impacts, leads some to argue that we need a defense system against any object larger than 200 meters diameter.

A major divergence of opinion concerns what our response to the impact threat should be. Most of the scientists involved in such assessments conclude that there is a significant risk and that governments should take some action (especially in searching for potential impactors), but that it is premature to build any defense systems in the absence of a specific identified threat. Others, the best known being Edward Teller (the father of the H-bomb), argue strongly for a more aggressive approach to asteroid defense. They would initiate experiments, eventually to include nuclear explosives, designed to learn more about how to deflect or destroy asteroids and comets. Some even advocate construction of a standing nuclear defense system to deal with the smaller impactors, for which the warning time might be short. But at least, they assert, we should start now to develop the technology for such a system.

These arguments concerning the magnitude of the threat and the most appropriate response make good TV and newspaper copy. They can lead to serious analyses of the various threats that we face on Earth and of the role of governments in dealing with potential disasters, both natural and human. All fit within the standard paradigm. But there is another viewpoint, held by a handful of British neo-catastrophists, that challenges this position.

The British Neo-Catastrophist School

The alternative viewpoint is advocated in its extreme form by astronomers Victor Clube and Bill Napier, who interpret historical records as indicating that Earth has been subject to extreme battering from space within the past few millennia. In their popular books The Cosmic Serpent and The Cosmic Winter, they take the position that the emergence of astrology in the western Mediterranean, the association of gods with planets in many ancient cultures, the widespread fear of comets and belief in angels, and many other aspects of our cultural and religious history are a reflection of massive bombardment of the planet a few thousand years ago. They further conclude that more recent historical events, including the collapse of the Roman Empire, the Dark Ages, and even the English Civil War, are related to climate changes induced by exceptional deposition of cosmic dust in Earth’s atmosphere. Although their historical analysis is suspiciously similar to that of Immanuel Velikovsky, Clube and Napier adamantly reject the association, arguing that unlike Velikovsky they root their explanations in sound physical and astronomical principles.

Supporting Clube and Napier are British astronomers Duncan Steel and Mark Bailey, who have concluded that the solar system is currently experiencing the aftermath of the break-up of a giant comet some millennia in the past. Our planet still intersects debris from this comet in what they call the Taurid complex of dust, small comets, and asteroids. They term this theory coherent catastrophism. Steel and Bailey estimate that the present lull in impacts will end in about a thousand years, when our orbit again crosses the denser parts of the Taurid complex, at which time the impact risk will rise by at least a factor of a hundred. All of these neo-catastrophists argue that urgent action is required to prevent the collapse of civilization under the next cosmic onslaught.

Most of us find these neo-catastrophist arguments difficult to swallow. Putting aside the issue of the Velikovskian interpretation of history and legend, the impact rate is still constrained by the cratering history of the Moon, which reflects the long-term average. If there are huge “spikes” in the frequency of impacts, produced by the break-up of giant comets, they must be compensated by much lower flux rates between peaks. Yet Clube, Steel, and their colleagues simultaneously assert that the consensus group underestimates the current impact rate, and that a big spike is coming. You can't have it both ways. If they are correct that almost all impacts occur during the spikes, then the present danger must be very low, and we have centuries to prepare to deal with the next peak. But they don't see it that way, and neither do the authors of several of the recent books.

Impact Science and Pseudoscience

While I believe that the British neo-catastrophists are wrong about the threat to Earth, their work is science, not pseudoscience. They are making their case to other scientists, and time will sort out who is right and who is wrong. They do, however, sometimes attract the attention of fringe elements. For example, the Society for Interdisciplinary Studies (SIS), a British group that espouses a skeptical philosophy but includes many defenders of Velikovskian ideas, is sponsoring a conference that features Clube and focuses on evidence for cosmic catastrophes in the ancient world. In fact, the work of Clube and Napier attracts many people who were once impressed by Velikovsky, such as Leroy Ellenberger, at one time a member of the Velikovsky inner circle and now one of the most outspoken critics of his current followers.

Every week I receive two or three inquiries from the public asking if some story they have read or heard about an imminent world-shattering impact is correct. These stories are not confined to the supermarket tabloids but have apparently attracted a following on the World Wide Web. Some people ask about a comet called Wormwood, with obvious reference to the apocalyptic vision in Revelation 8:10-11, when “the third angel sounded, and there fell a great star from heaven, burning as it were a lamp. . . . And the name of the star is called Wormwood.”

Then there is Comet Hale-Bopp. In November 1996 the press gave general coverage to a wild claim that this comet was accompanied by a spaceship and was headed toward an impact with Earth. (See Alan Hale, ”Hale-Bopp Comet Madness,” SI, March/April 1997.) The story apparently started when an amateur astronomer photographed the comet near a moderately bright star. In a curious logical progression he assumed the star was a spacecraft, that the spacecraft was at the same distance as the comet, and that the over-exposed stellar image represented the angular diameter of the craft, which would make it comparable in size to the giant planet Saturn. Others embellished the story by concluding that the spacecraft was traveling in the same orbit with the comet and that the trajectory was about to shift toward Earth. The mystery to me is why this fantasy was given serious media attention, even on a slow news day. I fear that we may see more of this sort of thing as the public becomes more aware of the threat of impacts.

Presenting the Issues to the Public

Of the ten books reviewed here, three are strongly in the Clube/Steel camp, and several of the others give their neo-catastrophism considerable attention. This is perhaps understandable, since these are the scientists who are most strongly claiming that the sky is falling. Besides, the connections they make between impacts and the more familiar fields of history and religion have an obvious public appeal.

In contrast, the public policy issues surrounding the development of a space defense system and the possible testing of nuclear explosives in space are barely touched on in most of these books. In part, this represents the secretive nature of the defense scientists, who (unlike the more gregarious astronomers) tend to avoid talking with journalists or appearing in TV documentaries. But the issues are real, and the first steps toward an asteroid defense are being initiated by the Pentagon’s just-approved Clementine 2 space mission to intercept three near-Earth asteroids and fire high-speed projectiles into their surfaces. It would be more useful if these policy questions, rather than the idea that cosmic dust caused the English Civil War, were being prominently addressed in public discussion of the impact threat.

On the positive side, the impact issue is proving to be an excellent vehicle for communicating some interesting aspects of contemporary science to the public. The topic, bringing together astronomy, environmental threats, and dinosaurs, is a natural. It focuses on the way historical science works (how can we figure out what really made the dinosaurs go extinct?), on the fragility of the environment (how can one small impact have global consequences?), on the nature of evolution (why were the mammals who succeeded the dinosaurs so different from them?), and on the nature of probability (if big impacts take place only once every million years, why worry now?). There is great potential here to teach good science as well as stimulate a useful public policy debate. Let’s hope these lofty goals are achieved in practice.

Artist’s concept of a catastrophic asteroid impact with Earth. Life near the impact would be instantly wiped out from the effects of high temperatures and pressures. Injection of huge masses of dust (and gases) into the atmosphere would effectively block out sunlight for long periods of time to the point that most life could not be sustained ("Nuclear Winter”). Painting by Don Davis, courtesy of NASA.

The Standard Reference on Impacts

In January 1993 more than one hundred experts met in Tucson, Arizona, to discuss all aspects of NEO impacts, from the extinction of the dinosaurs to the nature of impact-induced tsunamis to the deflection of an incoming asteroid by nuclear explosions. A wide spectrum of opinion was represented, as exemplified by the appearance of old antagonists Carl Sagan and Edward Teller on the same platform. In 1994 the edited, refereed product of this meeting was published by the University of Arizona Press, edited by Tom Gehrels, as Hazards Due to Comets and Asteroids. This 1,300-page book, with 120 authors, is the definitive reference on the impact hazard. Indeed, is it the only published source for much of the work, which has not appeared in technical journals. This is the best place to find detailed information on the subject, but more current reports are also on the World Wide Web at the Asteroid and Comet Impact Hazard Homepage (http://impact.arc.nasa.gov).

Books That Represent the Standard Paradigm

The following five books adhere generally to the standard view of the NEO impact threat, as represented in the NASA reports and the refereed conference volume Hazards Due to Comets and Asteroids.

John S. Lewis. Rain of Iron and Ice: The Very Real Threat of Comet and Asteroid Bombardment. Addison-Wesley, 1996, 236 pp., $25.00. John Lewis, professor of planetary science at the University of Arizona and one of the leading proponents of the use of asteroid resources for long-term space development, has written the best popular volume on the impact hazard. This book is written primarily for the scientifically literate lay audience, but it contains a great deal of information — and no small number of pointed barbs — directed toward scientific colleagues who study NEOs professionally. Lewis covers all the relevant issues of the nature of NEOs, the impact history of the solar system, the impact hazard, and mitigation. His writing style is compact, clear, and comprehensive.

In addition to his solid coverage of the basics, Lewis probes in depth three areas that are often missing in other treatments. (1) He clearly places Earth impacts in their broader solar-system context, with extensive discussion of the lessons learned from the cratering histories of the Moon, Mercury, and Venus. (2) He places strong emphasis on the long history of eyewitness reports of terrestrial bolides, meteorite showers, and atmospheric detonations, many of which have done considerable damage. This evidence, he stresses, is overlooked by most workers in the field. (3) He uses current models of the impact flux and the entry physics for impactors to “reconstruct” ten different one-century scenarios, with specific details of individual impacts and their damage, as a way to illustrate the variety of impact events. This same list allows Lewis to address the question of which scenarios (had they happened in the twentieth century) would likely have led to a widespread appreciation of the impact hazard and which scenarios probably would have been ignored or misinterpreted. The real history of the twentieth century is intermediate; Lewis argues that had the circumstances of the 1908 explosion of a 60-meter asteroid in the atmosphere over Siberia’s Stony Tunguska River been just a little different, we might never have known about it and foolishly continued to ignore the impact hazard up to the end of the century. (The Tunguska explosion flattened 2,000 square kilometers of forest and created a pressure wave recorded around the world.) This is the best introduction to the field, standing far above any of its competitors.

Dana Desonie. Cosmic Collisions. Henry Holt & Co. (A Scientific American Focus Book), 1996, 128 pp., $9.95. The Scientific American Focus Books are inexpensive paperbacks aimed at an intermediate or high school audience. Dana Desonie is a science writer with a doctorate in geochemistry. Her short, well-illustrated (in black and white) book is a straightforward introduction to cosmic impacts, beginning with solar-system formation, moving to comets and asteroids, then to Earth impacts (including the K-T event), Tunguska, current ideas about the impact hazard, and possible planetary defense. This is a serious, well-focused discussion that includes a lot of information in a book that can be read in a couple of hours.

David H. Levy. Impact Jupiter: The Crash of Comet Shoemaker-Levy 9. Plenum Press, 1995, 290 pp., $25.95. In this delightful memoir, writer and amateur astronomer David Levy provides a personal perspective on the history of Comet Shoemaker-Levy 9, from its discovery in the spring of 1993 until its death in July 1994. Writing for a lay audience, Levy tells with infectious enthusiasm of his adventures and those of many colleagues dealing with both the comet itself and the barrage of journalistic scrutiny it inspired. Only a few chapters concern the impact hazard, and defense issues are hardly mentioned, but Levy’s technical explanations are simple and clear. This is not a detailed reference work, and its real pleasure lies less in the science than in the many personal stories and the sense of involvement achieved by the diary-like presentation of events.

John Spencer and Jacqueline Mitton, editors. The Great Comet Crash: The Impact of Comet Shoemaker-Levy 9 on Jupiter. Cambridge University Press, 1995, 118 pp. John Spencer is a scientist at Lowell Observatory and an expert on Jupiter and its satellites; Jacqueline Mitton is a writer and Public Information Officer of the Royal Astronomical Society. They have collaborated to produce a timely and well-edited volume on the great comet impact, with chapters contributed by many of the leading researchers in their fields. Of all the books discussed here, this one has by far the best photographs, intelligently selected and beautifully reproduced. Only about a quarter of the book deals with the impact hazard, but these few chapters are by the experts and provide an excellent overview.

Philip M. Dauber and Richard A. Muller. The Three Big Bangs: Comet Crashes, Exploding Stars, and the Creation of the Universe. Addison-Wesley, 1996, 207 pp., $25.00. The first third (about seventy-five pages) of this popular-level book on modern astronomy is devoted to NEO impacts (and not just comets, as the title implies). The authors are physicists from the University of California at Berkeley, and Muller is one of the originators of the Nemesis hypothesis to explain periodicities in the terrestrial extinction record. Given the limited space available and the nonscientist audience toward which their book is aimed, Dauber and Muller do a good job of explaining the impact hazard story, with emphasis on the K-T extinction event and its lessons for the impact history of Earth. Both authors describe themselves as proteges of Luis Alvarez, and they are at their best in describing the events associated with the pioneering work that led to the identification of the extraterrestrial cause of the K-T event and the grand generalization of this evidence into a new theory of mass extinctions. In a few other areas, however, including discussions of the current hazard and of the Spaceguard Survey proposals, they oversimplify to the point of significant distortion. This book is a good read, but should be taken with quite a few grains of salt.

Books That Represent the British Neo-Catastrophist School

These three books by British authors all argue for a much higher level of danger from cosmic impacts and appeal to the record of the immediate past for evidence of the major role played by impacts in our history.

Duncan Steel. Rogue Asteroids and Doomsday Comets: The Search for the Million Megaton Menace That Threatens Life on Earth. Wiley, 1995, 308 pp., $24.95. Duncan Steel is well known in Australia and worldwide as a leader in NEO searches, a researcher on orbits of meteor streams, and a popularizer of the NEO impact risk. He writes well, and he covers all the issues of the nature of NEOs, the impact history of the solar system, the impact hazard, and mitigation. Roughly the first half of the book is on a par with Lewis and can be recommended with equal enthusiasm. In many other places, however, Steel departs dramatically from the mainstream to advocate the extreme neo-catastrophist position; in some places he admits that his positions are unorthodox or even bizarre, but elsewhere he neglects to make this distinction. Steel feels that the cratering flux is highly time-variable and states that “we are now fairly certain that terrestrial craters are, up to a large extent, formed during distinct periods of higher impactor flux.” In dynamics, he espouses the radical idea that “the main [asteroid] belt is not being depleted to supply meteorites and Earth-crossing asteroids, but quite the opposite.” He includes a highly personal chapter on the neo-catastrophist interpretation of Stonehenge that was characterized in another review (in Sky & Telescope) as “fiction, not even science fiction.” Perhaps some of these unorthodox ideas are deserving of serious scientific discussion, but their inclusion as fact in a popular-level book detracts significantly from its overall value, since the nonscientist reader has no way of separating the speculation from reliable information.

Gerrit L. Verschuur. Impact: The Threat of Comets and Asteroids. Oxford University Press, 1996, 237 pp., $25.00. Gerrit Verschuur, a well-known radio astronomer, educator, and author, presents a detailed (and very small print) discussion that lays out the full impact story. Throughout the book, Verschuur emphasizes data and interpretations that maximize the impact flux as well as the damage that can be done by impactors of a given yield. Since there are substantial uncertainties in many of these estimates, it is possible, by always selecting the worst case, to conclude that the danger is orders of magnitude greater than the values usually quoted. This is the tack taken by Verschuur, in general agreement with the arguments in Steel’s book reviewed above. Verschuur’s writing style is clear and witty, and I would happily recommend the first ninety-four pages. However, I cannot agree with the increasingly alarmist interpretations that dominate the book after page 95, on which Verschuur first introduces Clube and Napier. He argues that the “patterns in history” they have found should be the basis for policy decisions on protecting Earth from cosmic impacts, which he concludes produce worldwide flooding from asteroid impact every five thousand years or so. He writes that “we are perpetually poised on the edge of extinction and have been very lucky to get this far,” and “[t]he number of casualties resulting from an ocean impact . . . may be 10,000 times larger than given by Chapman and Morrison [in a 1994 paper in Nature].” In general, this book compares well with Steel’s, but with the same fatal flaw (from my perspective) of its emphasis on coherent catastrophism, and an even worse tendency to exaggerate the current impact hazard, often by several orders of magnitude.

John and Mary Gribbin. Fire on Earth: Doomsday, Dinosaurs, and Humankind. St. Martin’s Press, 1996, 264 pp., $23.95. British science writers John and Mary Gribbin have written a general overview of impacts and impact dangers for the lay public. Printed in large type and presented without illustrations, the book is significantly shorter than the two reviewed above, in spite of its similar page count. In essence, this book is a popularization of suggestions by Clube and Napier that human history has been greatly influenced by cosmic apparitions and cosmic impacts. They anticipate that “the world is in for another bout of fire from the heavens in about a thousand years’ time.” This is a pretty grim picture; hence their title, which literally refers to fires that may sweep Earth a few centuries in the future. The book contains a number of factual errors, but the main problem is that everything is slanted toward maximizing the impact flux and the associated danger. They assert that impact-associated atmospheric dust has been responsible for the recent ice ages, and that the climate of Earth today “rests on a knife edge,” ready to drop into another ice age with the smallest cosmic perturbation (no worry about global warming here!). This is a well-written book, but basically it adds little that is new. It seems to me that if one wants to explore the ideas of the British neo-catastrophist school, then one might just as well skip Gribbin and Gribbin and turn directly to the primary sources, in books by Clube and Napier and by Steel.

Unacceptable Books

The following two books should never have been published. The authors seem to be covering the field, but when you look in detail you find error and inconsistency on almost every page.

Patricia Barnes-Svarney. Asteroid: Earth Destroyer or New Frontier? Plenum Press, 1996, 292 pp., $25.95. Science writer and educator Patricia Barnes-Svarney has written an extremely frustrating book. She has attempted the ambitious task of covering for a lay audience the entire field of asteroid and comet studies, impacts, solar-system history, the hazard of Earth impacts, and the use of asteroids as space resources. Unfortunately, she is out of her depth in most of these areas, leading her repeatedly into conceptual and technical errors.

Barnes-Svarney loves technical jargon, mining the fields of astronomy, geology, and meteoritics for their numerous terms and then going on to invent a few of her own. Throughout the book she undercuts her own conclusions with words such as perhaps, seems, and probably even when she is reporting simple facts, as in the extreme example (p. 241) where she writes, “Right now, the best guess seems to be that there is no asteroid or comet known to be on an immediate collision course with the Earth.”

There is a lot of information in the book, but frequently it is presented as isolated “factoids,” rather than integrated into a self-consistent whole. For example, the author quotes half a dozen different values for the current terrestrial impact flux, but each in different units, so one cannot readily compare the results. Too often she gets things entirely backwards, as in her statement (p. 240), “Space scientists will tell you that everything within budgetary reason is now being done to search for more near-Earth asteroids.” I can't imagine any of the current observers, all of them starved for support, making such a statement. Barnes-Svarney also has some unusual opinions about NEO impacts. Although she writes at length about the K-T impact, she does not believe it played a role in the extinction of the dinosaurs; and even for other species, the most she says is that this impact is “thought to have helped in the Cretaceous-Tertiary extinctions.” Yet she credits impacts in the past with initiating plate tectonics, triggering volcanism, and generating Earth’s magnetic field — all highly dubious assertions. The book is especially weak in all things quantitative, riddled with inconsistencies and often misquoting sources.

Donald W. Cox and James H. Chestek. Doomsday Asteroid: Can We Survive? Prometheus Books, 1996, 338 pp., $26.95. The authors, popular science writer Don Cox and retired aerospace engineer James Chestek, have written about the impact hazard in the context of an argument for expanded human activity in space, including a major effort to visit the asteroids, colonize them, and mine them for space resources. Most of the factual material is from secondary sources such as Science News and the New York Times. The authors have obviously not attended any of the technical meetings on impacts held during the 1990s, and they do not understand many of the technical issues. From the beginning they tell us that the asteroids are most likely the result of an exploded planet, an idea that has had no scientific support for nearly fifty years. But this does not inhibit them from passing harsh judgment on the various teams of scientists who have participated in framing the NEO issue during the past five years. A special target of Cox and Chestek is the 1992 NASA Spaceguard strategy to search for asteroids, which they compare with the drunk who searches for his keys under the street lamp instead of where he lost them. They completely miss the point of carrying out a search to discover the objects as they periodically come close to Earth, but long before they actually hit. The direction from which they make their final approach is irrelevant. Because of this misunderstanding, they devote most of their search chapter to a simplistic argument that many impacting asteroids approach Earth from the sunward side, and on this basis they insist that a space system, with telescopes far from Earth, is required. The tone of much of the book is bitter and negative, and the attitude of the authors toward the research community is captured in the following paragraph:

An early warning space telescope certainly need not cost anywhere near as much money as the Hubble telescope. That was a research project, and many high-priced scientists and their graduate students spent many years charging their time to the project. Here we are discussing a simple early warning system, which the military knows how to build. The cost will only be for some engineering, not a lot of research, so it can be vastly cheaper.

The technical errors and widespread confusion displayed by Cox and Chestek in this book and by Patricia Barnes-Svarney her book reviewed above suggest that the filters against bad science writing for the public are not very effective. There seems to be no equivalent of peer review for science books, even at top publishers. Caveat emptor.